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 $188.86   9.388%   $206.5902   $206.59   $206.60   $206.60  
  Purchase #2 $59.72   10.105%   $65.7547   $65.75   $65.75   $65.80  
  Purchase #3 $187.44   9.357%   $204.9788   $204.98   $205.00   $205.00  
  Purchase #4 $93.39   8.441%   $101.273   $101.27   $101.25   $101.30  
  Purchase #5 $27.88   10.331%   $30.7603   $30.76   $30.75   $30.80  
  Purchase #6 $214.31   5.136%   $225.317   $225.32   $225.30   $225.30  
  Purchase #7 $88.60   10.212%   $97.6478   $97.65   $97.65   $97.60  
  7 purchase totals = $860.20       $932.3218   $932.32   $932.30   $932.40