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 $228.87   12.742%   $258.0326   $258.03   $258.05   $258.00  
  Purchase #2 $143.68   9.118%   $156.7807   $156.78   $156.80   $156.80  
  Purchase #3 $161.39   9.643%   $176.9528   $176.95   $176.95   $177.00  
  Purchase #4 $62.45   5.209%   $65.703   $65.70   $65.70   $65.70  
  Purchase #5 $37.73   7.752%   $40.6548   $40.65   $40.65   $40.70  
  Purchase #6 $171.93   13.397%   $194.9635   $194.96   $194.95   $195.00  
  Purchase #7 $182.79   13.429%   $207.3369   $207.34   $207.35   $207.30  
  7 purchase totals = $988.84       $1,100.4243   $1,100.41   $1,100.45   $1,100.50