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 $206.56   5.261%   $217.4271   $217.43   $217.45   $217.40  
  Purchase #2 $59.70   4.284%   $62.2575   $62.26   $62.25   $62.30  
  Purchase #3 $216.28   10.858%   $239.7637   $239.76   $239.75   $239.80  
  Purchase #4 $232.88   13.531%   $264.391   $264.39   $264.40   $264.40  
  Purchase #5 $189.98   5.679%   $200.769   $200.77   $200.75   $200.80  
  Purchase #6 $182.96   8.565%   $198.6305   $198.63   $198.65   $198.60  
  Purchase #7 $227.88   4.555%   $238.2599   $238.26   $238.25   $238.30  
  7 purchase totals = $1,316.24       $1,421.4987   $1,421.50   $1,421.50   $1,421.60