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 $81.25   13.241%   $92.0083   $92.01   $92.00   $92.00  
  Purchase #2 $81.57   12.326%   $91.6243   $91.62   $91.60   $91.60  
  Purchase #3 $56.75   9.539%   $62.1634   $62.16   $62.15   $62.20  
  Purchase #4 $183.55   6.644%   $195.7451   $195.75   $195.75   $195.70  
  Purchase #5 $61.67   11.345%   $68.6665   $68.67   $68.65   $68.70  
  Purchase #6 $205.78   4.714%   $215.4805   $215.48   $215.50   $215.50  
  Purchase #7 $91.28   11.198%   $101.5015   $101.50   $101.50   $101.50  
  7 purchase totals = $761.85       $827.1896   $827.19   $827.15   $827.20