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 $76.87   13.214%   $87.0276   $87.03   $87.05   $87.00  
  Purchase #2 $227.57   11.243%   $253.1557   $253.16   $253.15   $253.20  
  Purchase #3 $118.65   5.366%   $125.0168   $125.02   $125.00   $125.00  
  Purchase #4 $126.91   5.786%   $134.253   $134.25   $134.25   $134.30  
  Purchase #5 $59.93   4.632%   $62.706   $62.71   $62.70   $62.70  
  Purchase #6 $249.62   5.143%   $262.458   $262.46   $262.45   $262.50  
  Purchase #7 $38.48   8.633%   $41.802   $41.80   $41.80   $41.80  
  7 purchase totals = $898.03       $966.4191   $966.43   $966.40   $966.50