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	$244.83	12.712%	$275.9528	$275.95	$275.95	$276.00
Purchase #2	$98.29	13.590%	$111.6476	$111.65	$111.65	$111.60
Purchase #3	$190.30	11.671%	$212.5099	$212.51	$212.50	$212.50
Purchase #4	$91.72	8.126%	$99.1732	$99.17	$99.15	$99.20
Purchase #5	$59.65	11.541%	$66.5342	$66.53	$66.55	$66.50
Purchase #6	$70.37	10.698%	$77.8982	$77.90	$77.90	$77.90
Purchase #7	$244.27	10.860%	$270.7977	$270.80	$270.80	$270.80
7 purchase totals =	$999.43		$1,114.5136	$1,114.51	$1,114.50	$1,114.50