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	$47.31	6.657%	$50.4594	$50.46	$50.45	$50.50
Purchase #2	$129.59	12.371%	$145.6216	$145.62	$145.60	$145.60
Purchase #3	$230.61	11.413%	$256.9295	$256.93	$256.95	$256.90
Purchase #4	$145.97	13.645%	$165.8876	$165.89	$165.90	$165.90
Purchase #5	$45.38	9.831%	$49.8413	$49.84	$49.85	$49.80
Purchase #6	$186.58	13.221%	$211.2477	$211.25	$211.25	$211.20
Purchase #7	$131.61	4.385%	$137.3811	$137.38	$137.40	$137.40
7 purchase totals =	$917.05		$1,017.3682	$1,017.37	$1,017.40	$1,017.30