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 $175.65   13.328%   $199.0606   $199.06   $199.05   $199.10  
  Purchase #2 $173.73   8.369%   $188.2695   $188.27   $188.25   $188.30  
  Purchase #3 $52.47   3.752%   $54.4387   $54.44   $54.45   $54.40  
  Purchase #4 $191.86   3.531%   $198.6346   $198.63   $198.65   $198.60  
  Purchase #5 $139.90   8.517%   $151.8153   $151.82   $151.80   $151.80  
  Purchase #6 $249.50   5.792%   $263.951   $263.95   $263.95   $264.00  
  Purchase #7 $131.30   5.401%   $138.3915   $138.39   $138.40   $138.40  
  7 purchase totals = $1,114.41       $1,194.5612   $1,194.56   $1,194.55   $1,194.60