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 $32.39   8.818%   $35.2462   $35.25   $35.25   $35.20  
  Purchase #2 $169.43   6.191%   $179.9194   $179.92   $179.90   $179.90  
  Purchase #3 $212.68   8.142%   $229.9964   $230.00   $230.00   $230.00  
  Purchase #4 $204.39   4.513%   $213.6141   $213.61   $213.60   $213.60  
  Purchase #5 $101.54   6.694%   $108.3371   $108.34   $108.35   $108.30  
  Purchase #6 $54.43   8.661%   $59.1442   $59.14   $59.15   $59.10  
  Purchase #7 $194.82   11.725%   $217.6626   $217.66   $217.65   $217.70  
  7 purchase totals = $969.68       $1,043.9200   $1,043.92   $1,043.90   $1,043.80