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 $239.36   9.128%   $261.2088   $261.21   $261.20   $261.20  
  Purchase #2 $110.25   6.132%   $117.0105   $117.01   $117.00   $117.00  
  Purchase #3 $84.54   9.808%   $92.8317   $92.83   $92.85   $92.80  
  Purchase #4 $10.64   12.202%   $11.9383   $11.94   $11.95   $11.90  
  Purchase #5 $201.65   3.790%   $209.2925   $209.29   $209.30   $209.30  
  Purchase #6 $119.46   3.339%   $123.4488   $123.45   $123.45   $123.40  
  Purchase #7 $120.94   3.591%   $125.283   $125.28   $125.30   $125.30  
  7 purchase totals = $886.84       $941.0136   $941.01   $941.05   $940.90