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	$224.34	6.134%	$238.101	$238.10	$238.10	$238.10
Purchase #2	$185.29	9.194%	$202.3256	$202.33	$202.35	$202.30
Purchase #3	$200.89	6.275%	$213.4958	$213.50	$213.50	$213.50
Purchase #4	$208.57	6.872%	$222.9029	$222.90	$222.90	$222.90
Purchase #5	$128.55	9.238%	$140.4254	$140.43	$140.45	$140.40
Purchase #6	$222.47	8.370%	$241.0907	$241.09	$241.10	$241.10
Purchase #7	$237.84	7.225%	$255.0239	$255.02	$255.00	$255.00
7 purchase totals =	$1,407.95		$1,513.3653	$1,513.37	$1,513.40	$1,513.30