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 $83.75   12.834%   $94.4985   $94.50   $94.50   $94.50  
  Purchase #2 $137.63   7.507%   $147.9619   $147.96   $147.95   $148.00  
  Purchase #3 $140.59   12.866%   $158.6783   $158.68   $158.70   $158.70  
  Purchase #4 $101.53   7.633%   $109.2798   $109.28   $109.30   $109.30  
  Purchase #5 $63.53   6.692%   $67.7814   $67.78   $67.80   $67.80  
  Purchase #6 $231.86   3.111%   $239.0732   $239.07   $239.05   $239.10  
  Purchase #7 $83.60   5.687%   $88.3543   $88.35   $88.35   $88.40  
  7 purchase totals = $842.49       $905.6274   $905.62   $905.65   $905.80