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 $73.84   11.393%   $82.2526   $82.25   $82.25   $82.30  
  Purchase #2 $203.68   5.643%   $215.1737   $215.17   $215.15   $215.20  
  Purchase #3 $49.84   6.290%   $52.9749   $52.97   $52.95   $53.00  
  Purchase #4 $230.47   13.565%   $261.7333   $261.73   $261.75   $261.70  
  Purchase #5 $216.48   8.450%   $234.7726   $234.77   $234.75   $234.80  
  Purchase #6 $69.78   6.768%   $74.5027   $74.50   $74.50   $74.50  
  Purchase #7 $247.28   3.577%   $256.1252   $256.13   $256.15   $256.10  
  7 purchase totals = $1,091.37       $1,177.5350   $1,177.52   $1,177.50   $1,177.60