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 $55.33   4.862%   $58.0201   $58.02   $58.00   $58.00  
  Purchase #2 $118.64   4.804%   $124.3395   $124.34   $124.35   $124.30  
  Purchase #3 $177.60   5.484%   $187.3396   $187.34   $187.35   $187.30  
  Purchase #4 $22.33   5.648%   $23.5912   $23.59   $23.60   $23.60  
  Purchase #5 $138.68   12.274%   $155.7016   $155.70   $155.70   $155.70  
  Purchase #6 $111.38   10.662%   $123.2553   $123.26   $123.25   $123.30  
  Purchase #7 $115.92   8.616%   $125.9077   $125.91   $125.90   $125.90  
  7 purchase totals = $739.88       $798.1550   $798.16   $798.15   $798.10