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 $43.79   9.681%   $48.0293   $48.03   $48.05   $48.00  
  Purchase #2 $229.64   8.653%   $249.5107   $249.51   $249.50   $249.50  
  Purchase #3 $126.88   3.360%   $131.1432   $131.14   $131.15   $131.10  
  Purchase #4 $132.53   8.476%   $143.7632   $143.76   $143.75   $143.80  
  Purchase #5 $87.79   9.325%   $95.9764   $95.98   $96.00   $96.00  
  Purchase #6 $209.81   13.332%   $237.7819   $237.78   $237.80   $237.80  
  Purchase #7 $25.44   9.322%   $27.8115   $27.81   $27.80   $27.80  
  7 purchase totals = $855.88       $934.0162   $934.01   $934.05   $934.00