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	$111.31	8.302%	$120.551	$120.55	$120.55	$120.60
Purchase #2	$139.52	9.553%	$152.8483	$152.85	$152.85	$152.80
Purchase #3	$79.58	7.558%	$85.5947	$85.59	$85.60	$85.60
Purchase #4	$74.61	11.612%	$83.2737	$83.27	$83.25	$83.30
Purchase #5	$130.47	9.202%	$142.4758	$142.48	$142.50	$142.50
Purchase #6	$137.54	6.654%	$146.6919	$146.69	$146.70	$146.70
Purchase #7	$9.95	11.338%	$11.0781	$11.08	$11.10	$11.10
7 purchase totals =	$682.98		$742.5135	$742.51	$742.55	$742.60