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 $209.41   11.646%   $233.7979   $233.80   $233.80   $233.80  
  Purchase #2 $116.29   4.562%   $121.5951   $121.60   $121.60   $121.60  
  Purchase #3 $14.86   6.493%   $15.8249   $15.82   $15.80   $15.80  
  Purchase #4 $93.63   4.830%   $98.1523   $98.15   $98.15   $98.20  
  Purchase #5 $123.95   7.279%   $132.9723   $132.97   $132.95   $133.00  
  Purchase #6 $97.91   6.239%   $104.0186   $104.02   $104.00   $104.00  
  Purchase #7 $158.71   11.339%   $176.7061   $176.71   $176.70   $176.70  
  7 purchase totals = $814.76       $883.0672   $883.07   $883.00   $883.10