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 $179.62   11.142%   $199.6333   $199.63   $199.65   $199.60  
  Purchase #2 $206.73   3.158%   $213.2585   $213.26   $213.25   $213.30  
  Purchase #3 $116.46   7.583%   $125.2912   $125.29   $125.30   $125.30  
  Purchase #4 $97.36   13.643%   $110.6428   $110.64   $110.65   $110.60  
  Purchase #5 $216.38   7.569%   $232.7578   $232.76   $232.75   $232.80  
  Purchase #6 $230.25   10.442%   $254.2927   $254.29   $254.30   $254.30  
  Purchase #7 $215.91   11.519%   $240.7807   $240.78   $240.80   $240.80  
  7 purchase totals = $1,262.71       $1,376.6570   $1,376.65   $1,376.70   $1,376.70