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	$60.56	6.846%	$64.7059	$64.71	$64.70	$64.70
Purchase #2	$173.30	5.312%	$182.5057	$182.51	$182.50	$182.50
Purchase #3	$194.49	3.131%	$200.5795	$200.58	$200.60	$200.60
Purchase #4	$243.46	11.368%	$271.1365	$271.14	$271.15	$271.10
Purchase #5	$64.27	9.584%	$70.4296	$70.43	$70.45	$70.40
Purchase #6	$26.51	6.183%	$28.1491	$28.15	$28.15	$28.10
Purchase #7	$163.46	9.826%	$179.5216	$179.52	$179.50	$179.50
7 purchase totals =	$926.05		$997.0279	$997.04	$997.05	$996.90