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	$45.45	10.407%	$50.18	$50.18	$50.20	$50.20
Purchase #2	$62.33	12.466%	$70.1001	$70.10	$70.10	$70.10
Purchase #3	$35.58	10.199%	$39.2088	$39.21	$39.20	$39.20
Purchase #4	$146.68	10.693%	$162.3645	$162.36	$162.35	$162.40
Purchase #5	$229.66	3.847%	$238.495	$238.50	$238.50	$238.50
Purchase #6	$225.46	7.689%	$242.7956	$242.80	$242.80	$242.80
Purchase #7	$151.56	13.820%	$172.5056	$172.51	$172.50	$172.50
7 purchase totals =	$896.72		$975.6496	$975.66	$975.65	$975.70