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 $189.53   9.351%   $207.253   $207.25   $207.25   $207.30  
  Purchase #2 $33.37   3.228%   $34.4472   $34.45   $34.45   $34.40  
  Purchase #3 $109.39   8.777%   $118.9912   $118.99   $119.00   $119.00  
  Purchase #4 $161.84   8.130%   $174.9976   $175.00   $175.00   $175.00  
  Purchase #5 $38.76   6.811%   $41.3999   $41.40   $41.40   $41.40  
  Purchase #6 $146.71   13.863%   $167.0484   $167.05   $167.05   $167.00  
  Purchase #7 $148.66   8.439%   $161.2054   $161.21   $161.20   $161.20  
  7 purchase totals = $828.26       $905.3427   $905.35   $905.35   $905.30