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 $216.69   10.391%   $239.2063   $239.21   $239.20   $239.20  
  Purchase #2 $124.30   6.824%   $132.7822   $132.78   $132.80   $132.80  
  Purchase #3 $244.78   4.110%   $254.8405   $254.84   $254.85   $254.80  
  Purchase #4 $13.31   8.754%   $14.4752   $14.48   $14.50   $14.50  
  Purchase #5 $231.58   11.191%   $257.4961   $257.50   $257.50   $257.50  
  Purchase #6 $189.64   4.146%   $197.5025   $197.50   $197.50   $197.50  
  Purchase #7 $130.98   13.229%   $148.3073   $148.31   $148.30   $148.30  
  7 purchase totals = $1,151.28       $1,244.6101   $1,244.62   $1,244.65   $1,244.60