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	$156.67	3.485%	$162.1299	$162.13	$162.15	$162.10
Purchase #2	$61.96	8.642%	$67.3146	$67.31	$67.30	$67.30
Purchase #3	$187.42	12.325%	$210.5195	$210.52	$210.50	$210.50
Purchase #4	$28.58	4.706%	$29.925	$29.93	$29.95	$29.90
Purchase #5	$33.45	11.170%	$37.1864	$37.19	$37.20	$37.20
Purchase #6	$230.69	5.731%	$243.9108	$243.91	$243.90	$243.90
Purchase #7	$51.61	6.389%	$54.9074	$54.91	$54.90	$54.90
7 purchase totals =	$750.38		$805.8936	$805.90	$805.90	$805.80