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	$245.52	5.552%	$259.1513	$259.15	$259.15	$259.20
Purchase #2	$27.54	8.345%	$29.8382	$29.84	$29.85	$29.80
Purchase #3	$147.52	7.609%	$158.7448	$158.74	$158.75	$158.70
Purchase #4	$122.55	13.620%	$139.2413	$139.24	$139.25	$139.20
Purchase #5	$99.69	12.275%	$111.9269	$111.93	$111.95	$111.90
Purchase #6	$140.56	6.676%	$149.9438	$149.94	$149.95	$149.90
Purchase #7	$77.84	7.599%	$83.7551	$83.76	$83.75	$83.80
7 purchase totals =	$861.22		$932.6014	$932.60	$932.65	$932.50