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 $208.44   11.770%   $232.9734   $232.97   $232.95   $233.00  
  Purchase #2 $107.63   3.256%   $111.1344   $111.13   $111.15   $111.10  
  Purchase #3 $240.79   11.863%   $269.3549   $269.35   $269.35   $269.40  
  Purchase #4 $153.58   3.361%   $158.7418   $158.74   $158.75   $158.70  
  Purchase #5 $105.31   10.781%   $116.6635   $116.66   $116.65   $116.70  
  Purchase #6 $233.55   9.618%   $256.0128   $256.01   $256.00   $256.00  
  Purchase #7 $97.64   9.726%   $107.1365   $107.14   $107.15   $107.10  
  7 purchase totals = $1,146.94       $1,252.0173   $1,252.00   $1,252.00   $1,252.00