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 $82.56   6.560%   $87.9759   $87.98   $88.00   $88.00  
  Purchase #2 $113.84   8.378%   $123.3775   $123.38   $123.40   $123.40  
  Purchase #3 $87.68   11.368%   $97.6475   $97.65   $97.65   $97.60  
  Purchase #4 $17.79   5.630%   $18.7916   $18.79   $18.80   $18.80  
  Purchase #5 $79.83   7.136%   $85.5267   $85.53   $85.55   $85.50  
  Purchase #6 $47.75   13.396%   $54.1466   $54.15   $54.15   $54.10  
  Purchase #7 $118.46   6.579%   $126.2535   $126.25   $126.25   $126.30  
  7 purchase totals = $547.91       $593.7193   $593.73   $593.80   $593.70