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 $83.35   11.534%   $92.9636   $92.96   $92.95   $93.00  
  Purchase #2 $168.41   9.477%   $184.3702   $184.37   $184.35   $184.40  
  Purchase #3 $132.78   12.550%   $149.4439   $149.44   $149.45   $149.40  
  Purchase #4 $136.33   9.222%   $148.9024   $148.90   $148.90   $148.90  
  Purchase #5 $96.81   6.289%   $102.8984   $102.90   $102.90   $102.90  
  Purchase #6 $202.49   3.105%   $208.7773   $208.78   $208.80   $208.80  
  Purchase #7 $231.74   5.354%   $244.1474   $244.15   $244.15   $244.10  
  7 purchase totals = $1,051.91       $1,131.5032   $1,131.50   $1,131.50   $1,131.50