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 $185.61   13.573%   $210.8028   $210.80   $210.80   $210.80  
  Purchase #2 $114.33   7.868%   $123.3255   $123.33   $123.35   $123.30  
  Purchase #3 $88.97   7.473%   $95.6187   $95.62   $95.60   $95.60  
  Purchase #4 $136.79   10.612%   $151.3062   $151.31   $151.30   $151.30  
  Purchase #5 $213.99   6.370%   $227.6212   $227.62   $227.60   $227.60  
  Purchase #6 $119.63   9.329%   $130.7903   $130.79   $130.80   $130.80  
  Purchase #7 $47.80   12.343%   $53.7   $53.70   $53.70   $53.70  
  7 purchase totals = $907.12       $993.1647   $993.17   $993.15   $993.10