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	$74.56	10.609%	$82.4701	$82.47	$82.45	$82.50
Purchase #2	$69.54	4.846%	$72.9099	$72.91	$72.90	$72.90
Purchase #3	$44.37	13.452%	$50.3387	$50.34	$50.35	$50.30
Purchase #4	$67.49	7.829%	$72.7738	$72.77	$72.75	$72.80
Purchase #5	$240.50	8.199%	$260.2186	$260.22	$260.20	$260.20
Purchase #6	$29.75	3.765%	$30.8701	$30.87	$30.85	$30.90
Purchase #7	$165.64	7.170%	$177.5164	$177.52	$177.50	$177.50
7 purchase totals =	$691.85		$747.0976	$747.10	$747.00	$747.10