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 $163.78   11.554%   $182.7031   $182.70   $182.70   $182.70  
  Purchase #2 $90.93   9.203%   $99.2983   $99.30   $99.30   $99.30  
  Purchase #3 $27.58   11.510%   $30.7545   $30.75   $30.75   $30.80  
  Purchase #4 $148.90   6.220%   $158.1616   $158.16   $158.15   $158.20  
  Purchase #5 $247.84   13.232%   $280.6342   $280.63   $280.65   $280.60  
  Purchase #6 $232.44   7.546%   $249.9799   $249.98   $250.00   $250.00  
  Purchase #7 $55.26   6.352%   $58.7701   $58.77   $58.75   $58.80  
  7 purchase totals = $966.73       $1,060.3017   $1,060.29   $1,060.30   $1,060.40