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 $238.41   12.689%   $268.6618   $268.66   $268.65   $268.70  
  Purchase #2 $219.77   5.388%   $231.6112   $231.61   $231.60   $231.60  
  Purchase #3 $116.29   12.109%   $130.3716   $130.37   $130.35   $130.40  
  Purchase #4 $129.91   7.710%   $139.9261   $139.93   $139.95   $139.90  
  Purchase #5 $118.71   6.802%   $126.7847   $126.78   $126.80   $126.80  
  Purchase #6 $69.50   9.742%   $76.2707   $76.27   $76.25   $76.30  
  Purchase #7 $56.82   6.816%   $60.6929   $60.69   $60.70   $60.70  
  7 purchase totals = $949.41       $1,034.3190   $1,034.31   $1,034.30   $1,034.40