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 $195.35   8.357%   $211.6754   $211.68   $211.70   $211.70  
  Purchase #2 $67.37   13.421%   $76.4117   $76.41   $76.40   $76.40  
  Purchase #3 $67.69   10.689%   $74.9254   $74.93   $74.95   $74.90  
  Purchase #4 $58.59   6.193%   $62.2185   $62.22   $62.20   $62.20  
  Purchase #5 $186.73   10.175%   $205.7298   $205.73   $205.75   $205.70  
  Purchase #6 $58.38   10.162%   $64.3126   $64.31   $64.30   $64.30  
  Purchase #7 $237.94   4.857%   $249.4967   $249.50   $249.50   $249.50  
  7 purchase totals = $872.05       $944.7701   $944.78   $944.80   $944.70