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 $52.67   9.133%   $57.4804   $57.48   $57.50   $57.50  
  Purchase #2 $178.69   9.567%   $195.7853   $195.79   $195.80   $195.80  
  Purchase #3 $197.92   8.590%   $214.9213   $214.92   $214.90   $214.90  
  Purchase #4 $19.60   8.333%   $21.2333   $21.23   $21.25   $21.20  
  Purchase #5 $163.54   3.598%   $169.4242   $169.42   $169.40   $169.40  
  Purchase #6 $228.82   6.719%   $244.1944   $244.19   $244.20   $244.20  
  Purchase #7 $128.44   3.396%   $132.8018   $132.80   $132.80   $132.80  
  7 purchase totals = $969.68       $1,035.8407   $1,035.83   $1,035.85   $1,035.80