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 $65.30   5.434%   $68.8484   $68.85   $68.85   $68.80  
  Purchase #2 $63.55   4.156%   $66.1911   $66.19   $66.20   $66.20  
  Purchase #3 $194.33   3.723%   $201.5649   $201.56   $201.55   $201.60  
  Purchase #4 $188.27   3.274%   $194.434   $194.43   $194.45   $194.40  
  Purchase #5 $46.68   9.783%   $51.2467   $51.25   $51.25   $51.20  
  Purchase #6 $163.31   7.337%   $175.2921   $175.29   $175.30   $175.30  
  Purchase #7 $63.28   7.672%   $68.1348   $68.13   $68.15   $68.10  
  7 purchase totals = $784.72       $825.7120   $825.70   $825.75   $825.60