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	$60.33	11.417%	$67.2179	$67.22	$67.20	$67.20
Purchase #2	$149.95	5.652%	$158.4252	$158.43	$158.45	$158.40
Purchase #3	$130.55	4.322%	$136.1924	$136.19	$136.20	$136.20
Purchase #4	$58.33	10.478%	$64.4418	$64.44	$64.45	$64.40
Purchase #5	$94.60	6.397%	$100.6516	$100.65	$100.65	$100.70
Purchase #6	$222.87	9.401%	$243.822	$243.82	$243.80	$243.80
Purchase #7	$59.86	9.309%	$65.4324	$65.43	$65.45	$65.40
7 purchase totals =	$776.49		$836.1833	$836.18	$836.20	$836.10