Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $135.31   11.797%   $151.2725   $151.27   $151.25   $151.30  
  Purchase #2 $231.92   10.145%   $255.4483   $255.45   $255.45   $255.40  
  Purchase #3 $133.34   5.760%   $141.0204   $141.02   $141.00   $141.00  
  Purchase #4 $119.69   3.556%   $123.9462   $123.95   $123.95   $123.90  
  Purchase #5 $160.46   12.696%   $180.832   $180.83   $180.85   $180.80  
  Purchase #6 $132.47   4.432%   $138.3411   $138.34   $138.35   $138.30  
  Purchase #7 $186.68   13.186%   $211.2956   $211.30   $211.30   $211.30  
  7 purchase totals = $1,099.87       $1,202.1561   $1,202.16   $1,202.15   $1,202.00