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 $78.40   5.844%   $82.9817   $82.98   $83.00   $83.00  
  Purchase #2 $235.95   11.522%   $263.1362   $263.14   $263.15   $263.10  
  Purchase #3 $72.44   3.848%   $75.2275   $75.23   $75.25   $75.20  
  Purchase #4 $150.87   7.787%   $162.6182   $162.62   $162.60   $162.60  
  Purchase #5 $209.90   3.313%   $216.854   $216.85   $216.85   $216.90  
  Purchase #6 $59.77   11.749%   $66.7924   $66.79   $66.80   $66.80  
  Purchase #7 $112.80   11.566%   $125.8464   $125.85   $125.85   $125.80  
  7 purchase totals = $920.13       $993.4564   $993.46   $993.50   $993.40