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 $187.87   11.651%   $209.7587   $209.76   $209.75   $209.80  
  Purchase #2 $142.80   11.793%   $159.6404   $159.64   $159.65   $159.60  
  Purchase #3 $22.97   12.104%   $25.7503   $25.75   $25.75   $25.80  
  Purchase #4 $32.30   6.430%   $34.3769   $34.38   $34.40   $34.40  
  Purchase #5 $74.35   6.709%   $79.3381   $79.34   $79.35   $79.30  
  Purchase #6 $191.77   5.203%   $201.7478   $201.75   $201.75   $201.70  
  Purchase #7 $57.96   5.832%   $61.3402   $61.34   $61.35   $61.30  
  7 purchase totals = $710.02       $771.9524   $771.96   $772.00   $771.90