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 $184.68   6.376%   $196.4552   $196.46   $196.45   $196.50  
  Purchase #2 $151.61   8.117%   $163.9162   $163.92   $163.90   $163.90  
  Purchase #3 $62.74   5.526%   $66.207   $66.21   $66.20   $66.20  
  Purchase #4 $219.62   8.166%   $237.5542   $237.55   $237.55   $237.60  
  Purchase #5 $151.51   10.105%   $166.8201   $166.82   $166.80   $166.80  
  Purchase #6 $196.42   6.306%   $208.8062   $208.81   $208.80   $208.80  
  Purchase #7 $244.63   11.588%   $272.9777   $272.98   $273.00   $273.00  
  7 purchase totals = $1,211.21       $1,312.7366   $1,312.75   $1,312.70   $1,312.80