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	$161.88	5.377%	$170.5843	$170.58	$170.60	$170.60
Purchase #2	$40.73	3.710%	$42.2411	$42.24	$42.25	$42.20
Purchase #3	$64.37	12.693%	$72.5405	$72.54	$72.55	$72.50
Purchase #4	$11.80	7.178%	$12.647	$12.65	$12.65	$12.60
Purchase #5	$14.37	12.294%	$16.1366	$16.14	$16.15	$16.10
Purchase #6	$100.53	12.172%	$112.7665	$112.77	$112.75	$112.80
Purchase #7	$57.70	4.700%	$60.4119	$60.41	$60.40	$60.40
7 purchase totals =	$451.38		$487.3279	$487.33	$487.35	$487.20