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 $39.65   4.871%   $41.5814   $41.58   $41.60   $41.60  
  Purchase #2 $95.63   10.773%   $105.9322   $105.93   $105.95   $105.90  
  Purchase #3 $113.97   13.828%   $129.7298   $129.73   $129.75   $129.70  
  Purchase #4 $132.86   4.363%   $138.6567   $138.66   $138.65   $138.70  
  Purchase #5 $214.91   8.152%   $232.4295   $232.43   $232.45   $232.40  
  Purchase #6 $245.77   8.326%   $266.2328   $266.23   $266.25   $266.20  
  Purchase #7 $43.88   10.616%   $48.5383   $48.54   $48.55   $48.50  
  7 purchase totals = $886.67       $963.1007   $963.10   $963.20   $963.00