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 $228.94   6.329%   $243.4296   $243.43   $243.45   $243.40  
  Purchase #2 $8.45   3.507%   $8.7463   $8.75   $8.75   $8.70  
  Purchase #3 $55.68   10.176%   $61.346   $61.35   $61.35   $61.30  
  Purchase #4 $23.25   8.275%   $25.1739   $25.17   $25.15   $25.20  
  Purchase #5 $95.69   11.660%   $106.8475   $106.85   $106.85   $106.80  
  Purchase #6 $207.57   4.787%   $217.5064   $217.51   $217.50   $217.50  
  Purchase #7 $126.83   3.864%   $131.7307   $131.73   $131.75   $131.70  
  7 purchase totals = $746.41       $794.7804   $794.79   $794.80   $794.60