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 $59.85   13.115%   $67.6993   $67.70   $67.70   $67.70  
  Purchase #2 $71.32   4.661%   $74.6442   $74.64   $74.65   $74.60  
  Purchase #3 $101.31   6.184%   $107.575   $107.58   $107.60   $107.60  
  Purchase #4 $138.53   13.677%   $157.4767   $157.48   $157.50   $157.50  
  Purchase #5 $221.45   6.552%   $235.9594   $235.96   $235.95   $236.00  
  Purchase #6 $250.85   8.653%   $272.5561   $272.56   $272.55   $272.60  
  Purchase #7 $53.94   3.835%   $56.0086   $56.01   $56.00   $56.00  
  7 purchase totals = $897.25       $971.9193   $971.93   $971.95   $972.00