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 $237.98   11.159%   $264.5362   $264.54   $264.55   $264.50  
  Purchase #2 $6.49   12.191%   $7.2812   $7.28   $7.30   $7.30  
  Purchase #3 $90.99   3.677%   $94.3357   $94.34   $94.35   $94.30  
  Purchase #4 $88.39   4.755%   $92.5929   $92.59   $92.60   $92.60  
  Purchase #5 $202.85   3.732%   $210.4204   $210.42   $210.40   $210.40  
  Purchase #6 $206.69   4.422%   $215.8298   $215.83   $215.85   $215.80  
  Purchase #7 $118.99   5.691%   $125.7617   $125.76   $125.75   $125.80  
  7 purchase totals = $952.38       $1,010.7579   $1,010.76   $1,010.80   $1,010.70