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 $82.53   12.591%   $92.9214   $92.92   $92.90   $92.90  
  Purchase #2 $113.60   10.265%   $125.261   $125.26   $125.25   $125.30  
  Purchase #3 $133.92   11.533%   $149.365   $149.37   $149.35   $149.40  
  Purchase #4 $68.60   10.487%   $75.7941   $75.79   $75.80   $75.80  
  Purchase #5 $168.28   4.665%   $176.1303   $176.13   $176.15   $176.10  
  Purchase #6 $127.26   7.382%   $136.6543   $136.65   $136.65   $136.70  
  Purchase #7 $26.90   6.772%   $28.7217   $28.72   $28.70   $28.70  
  7 purchase totals = $721.09       $784.8478   $784.84   $784.80   $784.90