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 $180.69   11.582%   $201.6175   $201.62   $201.60   $201.60  
  Purchase #2 $29.47   13.573%   $33.47   $33.47   $33.45   $33.50  
  Purchase #3 $66.54   7.848%   $71.7621   $71.76   $71.75   $71.80  
  Purchase #4 $129.76   12.709%   $146.2512   $146.25   $146.25   $146.30  
  Purchase #5 $222.61   12.133%   $249.6193   $249.62   $249.60   $249.60  
  Purchase #6 $45.83   9.206%   $50.0491   $50.05   $50.05   $50.00  
  Purchase #7 $110.82   5.528%   $116.9461   $116.95   $116.95   $116.90  
  7 purchase totals = $785.72       $869.7153   $869.72   $869.65   $869.70