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	$67.44	10.162%	$74.2933	$74.29	$74.30	$74.30
Purchase #2	$102.77	8.681%	$111.6915	$111.69	$111.70	$111.70
Purchase #3	$50.74	9.496%	$55.5583	$55.56	$55.55	$55.60
Purchase #4	$14.90	6.464%	$15.8631	$15.86	$15.85	$15.90
Purchase #5	$92.59	9.633%	$101.5092	$101.51	$101.50	$101.50
Purchase #6	$190.56	10.260%	$210.1115	$210.11	$210.10	$210.10
Purchase #7	$16.54	7.819%	$17.8333	$17.83	$17.85	$17.80
7 purchase totals =	$535.54		$586.8602	$586.85	$586.85	$586.90