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 $212.99   13.472%   $241.684   $241.68   $241.70   $241.70  
  Purchase #2 $64.82   6.796%   $69.2252   $69.23   $69.25   $69.20  
  Purchase #3 $121.27   4.514%   $126.7441   $126.74   $126.75   $126.70  
  Purchase #4 $12.63   11.200%   $14.0446   $14.04   $14.05   $14.00  
  Purchase #5 $193.75   9.604%   $212.3578   $212.36   $212.35   $212.40  
  Purchase #6 $154.48   9.577%   $169.2745   $169.27   $169.25   $169.30  
  Purchase #7 $24.75   7.117%   $26.5115   $26.51   $26.50   $26.50  
  7 purchase totals = $784.69       $859.8417   $859.83   $859.85   $859.80