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	$186.55	13.870%	$212.4245	$212.42	$212.40	$212.40
Purchase #2	$165.59	3.700%	$171.7168	$171.72	$171.70	$171.70
Purchase #3	$47.84	5.833%	$50.6305	$50.63	$50.65	$50.60
Purchase #4	$155.58	7.670%	$167.513	$167.51	$167.50	$167.50
Purchase #5	$30.55	6.456%	$32.5223	$32.52	$32.50	$32.50
Purchase #6	$208.77	9.130%	$227.8307	$227.83	$227.85	$227.80
Purchase #7	$95.25	8.398%	$103.2491	$103.25	$103.25	$103.20
7 purchase totals =	$890.13		$965.8869	$965.88	$965.85	$965.70