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	$210.67	13.396%	$238.8914	$238.89	$238.90	$238.90
Purchase #2	$150.63	11.417%	$167.8274	$167.83	$167.85	$167.80
Purchase #3	$92.69	8.207%	$100.2971	$100.30	$100.30	$100.30
Purchase #4	$59.28	9.820%	$65.1013	$65.10	$65.10	$65.10
Purchase #5	$46.64	8.669%	$50.6832	$50.68	$50.70	$50.70
Purchase #6	$202.68	10.730%	$224.4276	$224.43	$224.45	$224.40
Purchase #7	$249.83	11.494%	$278.5455	$278.55	$278.55	$278.50
7 purchase totals =	$1,012.42		$1,125.7735	$1,125.78	$1,125.85	$1,125.70