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 $93.91   5.186%   $98.7802   $98.78   $98.80   $98.80  
  Purchase #2 $172.67   13.187%   $195.44   $195.44   $195.45   $195.40  
  Purchase #3 $138.94   13.680%   $157.947   $157.95   $157.95   $157.90  
  Purchase #4 $24.60   12.393%   $27.6487   $27.65   $27.65   $27.60  
  Purchase #5 $56.82   4.155%   $59.1809   $59.18   $59.20   $59.20  
  Purchase #6 $72.47   4.338%   $75.6137   $75.61   $75.60   $75.60  
  Purchase #7 $212.34   11.233%   $236.1922   $236.19   $236.20   $236.20  
  7 purchase totals = $771.75       $850.8027   $850.80   $850.85   $850.70