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 $220.98   9.431%   $241.8206   $241.82   $241.80   $241.80  
  Purchase #2 $224.95   4.601%   $235.2999   $235.30   $235.30   $235.30  
  Purchase #3 $62.63   13.574%   $71.1314   $71.13   $71.15   $71.10  
  Purchase #4 $7.25   8.482%   $7.8649   $7.86   $7.85   $7.90  
  Purchase #5 $133.32   5.785%   $141.0326   $141.03   $141.05   $141.00  
  Purchase #6 $66.75   13.494%   $75.7572   $75.76   $75.75   $75.80  
  Purchase #7 $158.27   6.469%   $168.5085   $168.51   $168.50   $168.50  
  7 purchase totals = $874.15       $941.4151   $941.41   $941.40   $941.40