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 $68.67   11.606%   $76.6398   $76.64   $76.65   $76.60  
  Purchase #2 $107.32   11.509%   $119.6715   $119.67   $119.65   $119.70  
  Purchase #3 $160.44   12.550%   $180.5752   $180.58   $180.60   $180.60  
  Purchase #4 $116.75   8.122%   $126.2324   $126.23   $126.25   $126.20  
  Purchase #5 $196.55   7.199%   $210.6996   $210.70   $210.70   $210.70  
  Purchase #6 $63.86   13.735%   $72.6312   $72.63   $72.65   $72.60  
  Purchase #7 $249.46   4.267%   $260.1045   $260.10   $260.10   $260.10  
  7 purchase totals = $963.05       $1,046.5542   $1,046.55   $1,046.60   $1,046.50