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 $237.51   6.863%   $253.8103   $253.81   $253.80   $253.80  
  Purchase #2 $62.67   5.574%   $66.1632   $66.16   $66.15   $66.20  
  Purchase #3 $247.46   10.571%   $273.619   $273.62   $273.60   $273.60  
  Purchase #4 $192.81   6.862%   $206.0406   $206.04   $206.05   $206.00  
  Purchase #5 $91.30   6.172%   $96.935   $96.94   $96.95   $96.90  
  Purchase #6 $240.65   4.662%   $251.8691   $251.87   $251.85   $251.90  
  Purchase #7 $239.29   4.166%   $249.2588   $249.26   $249.25   $249.30  
  7 purchase totals = $1,311.69       $1,397.6960   $1,397.70   $1,397.65   $1,397.70