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 $249.78   7.770%   $269.1879   $269.19   $269.20   $269.20  
  Purchase #2 $117.44   12.564%   $132.1952   $132.20   $132.20   $132.20  
  Purchase #3 $16.83   4.765%   $17.6319   $17.63   $17.65   $17.60  
  Purchase #4 $41.91   3.863%   $43.529   $43.53   $43.55   $43.50  
  Purchase #5 $126.68   3.620%   $131.2658   $131.27   $131.25   $131.30  
  Purchase #6 $8.35   11.318%   $9.2951   $9.30   $9.30   $9.30  
  Purchase #7 $65.27   10.772%   $72.3009   $72.30   $72.30   $72.30  
  7 purchase totals = $626.26       $675.4058   $675.42   $675.45   $675.40