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 $74.98   11.813%   $83.8374   $83.84   $83.85   $83.80  
  Purchase #2 $211.58   7.643%   $227.7511   $227.75   $227.75   $227.80  
  Purchase #3 $247.92   3.720%   $257.1426   $257.14   $257.15   $257.10  
  Purchase #4 $85.95   11.131%   $95.5171   $95.52   $95.50   $95.50  
  Purchase #5 $5.95   6.625%   $6.3442   $6.34   $6.35   $6.30  
  Purchase #6 $49.49   8.308%   $53.6016   $53.60   $53.60   $53.60  
  Purchase #7 $220.84   11.263%   $245.7132   $245.71   $245.70   $245.70  
  7 purchase totals = $896.71       $969.9072   $969.90   $969.90   $969.80