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 $196.33   6.416%   $208.9265   $208.93   $208.95   $208.90  
  Purchase #2 $204.57   6.493%   $217.8527   $217.85   $217.85   $217.90  
  Purchase #3 $222.94   10.861%   $247.1535   $247.15   $247.15   $247.20  
  Purchase #4 $209.70   5.230%   $220.6673   $220.67   $220.65   $220.70  
  Purchase #5 $153.44   4.683%   $160.6256   $160.63   $160.65   $160.60  
  Purchase #6 $121.25   6.872%   $129.5823   $129.58   $129.60   $129.60  
  Purchase #7 $118.75   11.412%   $132.3018   $132.30   $132.30   $132.30  
  7 purchase totals = $1,226.98       $1,317.1097   $1,317.11   $1,317.15   $1,317.20