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 $87.33   6.644%   $93.1322   $93.13   $93.15   $93.10  
  Purchase #2 $92.56   10.108%   $101.916   $101.92   $101.90   $101.90  
  Purchase #3 $166.54   9.695%   $182.6861   $182.69   $182.70   $182.70  
  Purchase #4 $167.96   6.105%   $178.214   $178.21   $178.20   $178.20  
  Purchase #5 $250.37   8.171%   $270.8277   $270.83   $270.85   $270.80  
  Purchase #6 $214.47   10.284%   $236.5261   $236.53   $236.55   $236.50  
  Purchase #7 $176.63   11.142%   $196.3101   $196.31   $196.30   $196.30  
  7 purchase totals = $1,155.86       $1,259.6122   $1,259.62   $1,259.65   $1,259.50