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	$246.95	11.181%	$274.5615	$274.56	$274.55	$274.60
Purchase #2	$18.69	7.483%	$20.0886	$20.09	$20.10	$20.10
Purchase #3	$107.84	9.574%	$118.1646	$118.16	$118.15	$118.20
Purchase #4	$127.71	12.810%	$144.0697	$144.07	$144.05	$144.10
Purchase #5	$105.90	8.524%	$114.9269	$114.93	$114.95	$114.90
Purchase #6	$145.61	11.123%	$161.8062	$161.81	$161.80	$161.80
Purchase #7	$42.43	6.621%	$45.2393	$45.24	$45.25	$45.20
7 purchase totals =	$795.13		$878.8568	$878.86	$878.85	$878.90