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 $52.79   13.605%   $59.9721   $59.97   $59.95   $60.00  
  Purchase #2 $86.93   8.624%   $94.4268   $94.43   $94.45   $94.40  
  Purchase #3 $105.79   6.289%   $112.4431   $112.44   $112.45   $112.40  
  Purchase #4 $230.56   5.340%   $242.8719   $242.87   $242.85   $242.90  
  Purchase #5 $10.92   12.453%   $12.2799   $12.28   $12.30   $12.30  
  Purchase #6 $70.44   7.473%   $75.704   $75.70   $75.70   $75.70  
  Purchase #7 $9.78   11.449%   $10.8997   $10.90   $10.90   $10.90  
  7 purchase totals = $567.21       $608.5975   $608.59   $608.60   $608.60