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 $52.34   12.549%   $58.9081   $58.91   $58.90   $58.90  
  Purchase #2 $150.36   6.791%   $160.5709   $160.57   $160.55   $160.60  
  Purchase #3 $118.58   5.761%   $125.4114   $125.41   $125.40   $125.40  
  Purchase #4 $158.70   4.207%   $165.3765   $165.38   $165.40   $165.40  
  Purchase #5 $86.59   7.232%   $92.8522   $92.85   $92.85   $92.90  
  Purchase #6 $119.60   4.356%   $124.8098   $124.81   $124.80   $124.80  
  Purchase #7 $163.81   8.435%   $177.6274   $177.63   $177.65   $177.60  
  7 purchase totals = $849.98       $905.5563   $905.56   $905.55   $905.60