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 $188.58   11.515%   $210.295   $210.30   $210.30   $210.30  
  Purchase #2 $88.63   7.381%   $95.1718   $95.17   $95.15   $95.20  
  Purchase #3 $191.61   13.588%   $217.646   $217.65   $217.65   $217.60  
  Purchase #4 $118.48   6.643%   $126.3506   $126.35   $126.35   $126.40  
  Purchase #5 $114.45   4.581%   $119.693   $119.69   $119.70   $119.70  
  Purchase #6 $129.58   13.214%   $146.7027   $146.70   $146.70   $146.70  
  Purchase #7 $107.25   9.106%   $117.0162   $117.02   $117.00   $117.00  
  7 purchase totals = $938.58       $1,032.8753   $1,032.88   $1,032.85   $1,032.90