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	$243.60	11.291%	$271.1049	$271.10	$271.10	$271.10
Purchase #2	$26.63	9.375%	$29.1266	$29.13	$29.15	$29.10
Purchase #3	$75.53	3.157%	$77.9145	$77.91	$77.90	$77.90
Purchase #4	$197.30	12.762%	$222.4794	$222.48	$222.50	$222.50
Purchase #5	$6.45	10.729%	$7.142	$7.14	$7.15	$7.10
Purchase #6	$199.52	11.616%	$222.6962	$222.70	$222.70	$222.70
Purchase #7	$197.75	11.640%	$220.7681	$220.77	$220.75	$220.80
7 purchase totals =	$946.78		$1,051.2317	$1,051.23	$1,051.25	$1,051.20