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 $111.73   6.863%   $119.398   $119.40   $119.40   $119.40  
  Purchase #2 $228.94   11.792%   $255.9366   $255.94   $255.95   $255.90  
  Purchase #3 $113.55   4.141%   $118.2521   $118.25   $118.25   $118.30  
  Purchase #4 $32.81   4.504%   $34.2878   $34.29   $34.30   $34.30  
  Purchase #5 $67.56   9.272%   $73.8242   $73.82   $73.80   $73.80  
  Purchase #6 $161.32   7.261%   $173.0334   $173.03   $173.05   $173.00  
  Purchase #7 $228.84   8.463%   $248.2067   $248.21   $248.20   $248.20  
  7 purchase totals = $944.75       $1,022.9388   $1,022.94   $1,022.95   $1,022.90