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	$245.33	13.631%	$278.7709	$278.77	$278.75	$278.80
Purchase #2	$194.35	10.343%	$214.4516	$214.45	$214.45	$214.50
Purchase #3	$133.39	6.666%	$142.2818	$142.28	$142.30	$142.30
Purchase #4	$44.31	9.374%	$48.4636	$48.46	$48.45	$48.50
Purchase #5	$102.74	4.354%	$107.2133	$107.21	$107.20	$107.20
Purchase #6	$37.66	12.310%	$42.2959	$42.30	$42.30	$42.30
Purchase #7	$223.69	4.210%	$233.1073	$233.11	$233.10	$233.10
7 purchase totals =	$981.47		$1,066.5844	$1,066.58	$1,066.55	$1,066.70