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 $154.65   3.176%   $159.5617   $159.56   $159.55   $159.60  
  Purchase #2 $163.85   3.627%   $169.7928   $169.79   $169.80   $169.80  
  Purchase #3 $102.61   8.369%   $111.1974   $111.20   $111.20   $111.20  
  Purchase #4 $146.57   11.801%   $163.8667   $163.87   $163.85   $163.90  
  Purchase #5 $9.52   7.638%   $10.2471   $10.25   $10.25   $10.20  
  Purchase #6 $18.25   8.609%   $19.8211   $19.82   $19.80   $19.80  
  Purchase #7 $159.66   11.394%   $177.8517   $177.85   $177.85   $177.90  
  7 purchase totals = $755.11       $812.3385   $812.34   $812.30   $812.40