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 $208.83   11.392%   $232.6199   $232.62   $232.60   $232.60  
  Purchase #2 $187.48   4.140%   $195.2417   $195.24   $195.25   $195.20  
  Purchase #3 $104.42   6.813%   $111.5341   $111.53   $111.55   $111.50  
  Purchase #4 $187.55   9.447%   $205.2678   $205.27   $205.25   $205.30  
  Purchase #5 $242.73   5.179%   $255.301   $255.30   $255.30   $255.30  
  Purchase #6 $50.28   9.258%   $54.9349   $54.93   $54.95   $54.90  
  Purchase #7 $126.27   11.589%   $140.9034   $140.90   $140.90   $140.90  
  7 purchase totals = $1,107.56       $1,195.8028   $1,195.79   $1,195.80   $1,195.70