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 $10.29   6.473%   $10.9561   $10.96   $10.95   $11.00  
  Purchase #2 $196.58   7.209%   $210.7515   $210.75   $210.75   $210.80  
  Purchase #3 $155.72   3.323%   $160.8946   $160.89   $160.90   $160.90  
  Purchase #4 $219.49   5.457%   $231.4676   $231.47   $231.45   $231.50  
  Purchase #5 $180.44   11.622%   $201.4107   $201.41   $201.40   $201.40  
  Purchase #6 $218.56   11.654%   $244.031   $244.03   $244.05   $244.00  
  Purchase #7 $185.92   11.683%   $207.641   $207.64   $207.65   $207.60  
  7 purchase totals = $1,167.00       $1,267.1525   $1,267.15   $1,267.15   $1,267.20