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 $245.88   8.739%   $267.3675   $267.37   $267.35   $267.40  
  Purchase #2 $117.77   9.593%   $129.0677   $129.07   $129.05   $129.10  
  Purchase #3 $226.82   6.474%   $241.5043   $241.50   $241.50   $241.50  
  Purchase #4 $225.56   4.674%   $236.1027   $236.10   $236.10   $236.10  
  Purchase #5 $217.95   7.376%   $234.026   $234.03   $234.05   $234.00  
  Purchase #6 $9.47   11.749%   $10.5826   $10.58   $10.60   $10.60  
  Purchase #7 $237.91   3.226%   $245.585   $245.59   $245.60   $245.60  
  7 purchase totals = $1,281.36       $1,364.2358   $1,364.24   $1,364.25   $1,364.30