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 $96.52   8.354%   $104.5833   $104.58   $104.60   $104.60  
  Purchase #2 $66.51   9.684%   $72.9508   $72.95   $72.95   $73.00  
  Purchase #3 $155.89   12.170%   $174.8618   $174.86   $174.85   $174.90  
  Purchase #4 $226.68   5.864%   $239.9725   $239.97   $239.95   $240.00  
  Purchase #5 $98.94   3.446%   $102.3495   $102.35   $102.35   $102.30  
  Purchase #6 $154.29   8.175%   $166.9032   $166.90   $166.90   $166.90  
  Purchase #7 $86.99   11.676%   $97.147   $97.15   $97.15   $97.10  
  7 purchase totals = $885.82       $958.7681   $958.76   $958.75   $958.80