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 $186.54   11.234%   $207.4959   $207.50   $207.50   $207.50  
  Purchase #2 $194.90   9.674%   $213.7546   $213.75   $213.75   $213.80  
  Purchase #3 $222.46   6.489%   $236.8954   $236.90   $236.90   $236.90  
  Purchase #4 $161.93   8.334%   $175.4252   $175.43   $175.45   $175.40  
  Purchase #5 $245.60   12.167%   $275.4822   $275.48   $275.50   $275.50  
  Purchase #6 $180.95   8.659%   $196.6185   $196.62   $196.60   $196.60  
  Purchase #7 $189.31   8.120%   $204.682   $204.68   $204.70   $204.70  
  7 purchase totals = $1,381.69       $1,510.3538   $1,510.36   $1,510.40   $1,510.40