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	$173.75	8.658%	$188.7933	$188.79	$188.80	$188.80
Purchase #2	$107.80	6.404%	$114.7035	$114.70	$114.70	$114.70
Purchase #3	$38.67	8.790%	$42.0691	$42.07	$42.05	$42.10
Purchase #4	$80.89	5.204%	$85.0995	$85.10	$85.10	$85.10
Purchase #5	$137.94	10.588%	$152.5451	$152.55	$152.55	$152.50
Purchase #6	$172.60	13.245%	$195.4609	$195.46	$195.45	$195.50
Purchase #7	$61.82	9.399%	$67.6305	$67.63	$67.65	$67.60
7 purchase totals =	$773.47		$846.3019	$846.30	$846.30	$846.30