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 $84.94   12.484%   $95.5439   $95.54   $95.55   $95.50  
  Purchase #2 $126.55   13.273%   $143.347   $143.35   $143.35   $143.30  
  Purchase #3 $114.66   5.594%   $121.0741   $121.07   $121.05   $121.10  
  Purchase #4 $16.86   12.228%   $18.9216   $18.92   $18.90   $18.90  
  Purchase #5 $250.34   13.805%   $284.8994   $284.90   $284.90   $284.90  
  Purchase #6 $202.43   11.758%   $226.2317   $226.23   $226.25   $226.20  
  Purchase #7 $101.59   11.216%   $112.9843   $112.98   $113.00   $113.00  
  7 purchase totals = $897.37       $1,003.0020   $1,002.99   $1,003.00   $1,002.90