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 $248.61   8.272%   $269.175   $269.18   $269.20   $269.20  
  Purchase #2 $246.73   3.463%   $255.2743   $255.27   $255.25   $255.30  
  Purchase #3 $195.68   9.249%   $213.7784   $213.78   $213.80   $213.80  
  Purchase #4 $50.55   6.201%   $53.6846   $53.68   $53.70   $53.70  
  Purchase #5 $84.50   12.144%   $94.7617   $94.76   $94.75   $94.80  
  Purchase #6 $27.67   11.535%   $30.8617   $30.86   $30.85   $30.90  
  Purchase #7 $219.68   6.483%   $233.9219   $233.92   $233.90   $233.90  
  7 purchase totals = $1,073.42       $1,151.4576   $1,151.45   $1,151.45   $1,151.60