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	$212.67	8.308%	$230.3386	$230.34	$230.35	$230.30
Purchase #2	$152.84	4.588%	$159.8523	$159.85	$159.85	$159.90
Purchase #3	$56.51	9.108%	$61.6569	$61.66	$61.65	$61.70
Purchase #4	$29.55	13.137%	$33.432	$33.43	$33.45	$33.40
Purchase #5	$246.40	13.742%	$280.2603	$280.26	$280.25	$280.30
Purchase #6	$210.67	5.438%	$222.1262	$222.13	$222.15	$222.10
Purchase #7	$170.93	8.551%	$185.5462	$185.55	$185.55	$185.50
7 purchase totals =	$1,079.57		$1,173.2125	$1,173.22	$1,173.25	$1,173.20