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 $95.75   9.149%   $104.5102   $104.51   $104.50   $104.50  
  Purchase #2 $105.31   3.176%   $108.6546   $108.65   $108.65   $108.70  
  Purchase #3 $83.71   11.218%   $93.1006   $93.10   $93.10   $93.10  
  Purchase #4 $24.61   11.206%   $27.3678   $27.37   $27.35   $27.40  
  Purchase #5 $84.64   8.576%   $91.8987   $91.90   $91.90   $91.90  
  Purchase #6 $163.57   10.230%   $180.3032   $180.30   $180.30   $180.30  
  Purchase #7 $93.27   5.616%   $98.508   $98.51   $98.50   $98.50  
  7 purchase totals = $650.86       $704.3431   $704.34   $704.30   $704.40