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 $241.89   7.633%   $260.3535   $260.35   $260.35   $260.40  
  Purchase #2 $118.33   6.842%   $126.4261   $126.43   $126.45   $126.40  
  Purchase #3 $219.42   8.229%   $237.4761   $237.48   $237.50   $237.50  
  Purchase #4 $58.31   3.785%   $60.517   $60.52   $60.50   $60.50  
  Purchase #5 $11.65   5.496%   $12.2903   $12.29   $12.30   $12.30  
  Purchase #6 $60.84   10.312%   $67.1138   $67.11   $67.10   $67.10  
  Purchase #7 $135.58   4.723%   $141.9834   $141.98   $142.00   $142.00  
  7 purchase totals = $846.02       $906.1602   $906.16   $906.20   $906.20