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	$234.82	4.397%	$245.145	$245.15	$245.15	$245.10
Purchase #2	$128.39	3.666%	$133.0968	$133.10	$133.10	$133.10
Purchase #3	$239.45	6.709%	$255.5147	$255.51	$255.50	$255.50
Purchase #4	$223.97	8.248%	$242.443	$242.44	$242.45	$242.40
Purchase #5	$39.75	13.847%	$45.2542	$45.25	$45.25	$45.30
Purchase #6	$175.89	6.748%	$187.7591	$187.76	$187.75	$187.80
Purchase #7	$142.49	13.268%	$161.3956	$161.40	$161.40	$161.40
7 purchase totals =	$1,184.76		$1,270.6084	$1,270.61	$1,270.60	$1,270.60