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 $76.62   11.648%   $85.5447   $85.54   $85.55   $85.50  
  Purchase #2 $202.58   13.266%   $229.4543   $229.45   $229.45   $229.50  
  Purchase #3 $63.76   5.172%   $67.0577   $67.06   $67.05   $67.10  
  Purchase #4 $83.79   10.161%   $92.3039   $92.30   $92.30   $92.30  
  Purchase #5 $116.39   8.742%   $126.5648   $126.56   $126.55   $126.60  
  Purchase #6 $248.82   7.696%   $267.9692   $267.97   $267.95   $268.00  
  Purchase #7 $188.46   9.547%   $206.4523   $206.45   $206.45   $206.50  
  7 purchase totals = $980.42       $1,075.3469   $1,075.33   $1,075.30   $1,075.50