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 $248.79   6.424%   $264.7723   $264.77   $264.75   $264.80  
  Purchase #2 $239.38   11.187%   $266.1594   $266.16   $266.15   $266.20  
  Purchase #3 $118.76   13.580%   $134.8876   $134.89   $134.90   $134.90  
  Purchase #4 $139.98   6.605%   $149.2257   $149.23   $149.25   $149.20  
  Purchase #5 $198.70   3.388%   $205.432   $205.43   $205.45   $205.40  
  Purchase #6 $99.65   5.162%   $104.7939   $104.79   $104.80   $104.80  
  Purchase #7 $33.73   8.776%   $36.6901   $36.69   $36.70   $36.70  
  7 purchase totals = $1,078.99       $1,161.9610   $1,161.96   $1,162.00   $1,162.00