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 $205.77   10.684%   $227.7545   $227.75   $227.75   $227.80  
  Purchase #2 $118.69   6.105%   $125.936   $125.94   $125.95   $125.90  
  Purchase #3 $61.63   9.479%   $67.4719   $67.47   $67.45   $67.50  
  Purchase #4 $21.65   9.685%   $23.7468   $23.75   $23.75   $23.70  
  Purchase #5 $27.97   9.187%   $30.5396   $30.54   $30.55   $30.50  
  Purchase #6 $61.69   13.371%   $69.9386   $69.94   $69.95   $69.90  
  Purchase #7 $243.57   4.494%   $254.516   $254.52   $254.50   $254.50  
  7 purchase totals = $740.97       $799.9034   $799.91   $799.90   $799.80