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 $60.48   9.420%   $66.1772   $66.18   $66.20   $66.20  
  Purchase #2 $191.79   11.369%   $213.5946   $213.59   $213.60   $213.60  
  Purchase #3 $154.94   5.485%   $163.4385   $163.44   $163.45   $163.40  
  Purchase #4 $26.96   7.681%   $29.0308   $29.03   $29.05   $29.00  
  Purchase #5 $136.58   5.448%   $144.0209   $144.02   $144.00   $144.00  
  Purchase #6 $36.52   13.849%   $41.5777   $41.58   $41.60   $41.60  
  Purchase #7 $217.97   3.214%   $224.9756   $224.98   $225.00   $225.00  
  7 purchase totals = $825.24       $882.8153   $882.82   $882.90   $882.80