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 $238.25   9.548%   $260.9981   $261.00   $261.00   $261.00  
  Purchase #2 $113.53   4.761%   $118.9352   $118.94   $118.95   $118.90  
  Purchase #3 $11.53   13.799%   $13.121   $13.12   $13.10   $13.10  
  Purchase #4 $158.78   11.748%   $177.4335   $177.43   $177.45   $177.40  
  Purchase #5 $179.89   8.585%   $195.3336   $195.33   $195.35   $195.30  
  Purchase #6 $163.45   3.248%   $168.7589   $168.76   $168.75   $168.80  
  Purchase #7 $22.84   8.807%   $24.8515   $24.85   $24.85   $24.90  
  7 purchase totals = $888.27       $959.4318   $959.43   $959.45   $959.40