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	$246.74	11.633%	$275.4433	$275.44	$275.45	$275.40
Purchase #2	$78.75	5.532%	$83.1065	$83.11	$83.10	$83.10
Purchase #3	$233.68	7.178%	$250.4536	$250.45	$250.45	$250.50
Purchase #4	$6.93	3.144%	$7.1479	$7.15	$7.15	$7.10
Purchase #5	$47.60	4.683%	$49.8291	$49.83	$49.85	$49.80
Purchase #6	$144.49	4.259%	$150.6438	$150.64	$150.65	$150.60
Purchase #7	$129.30	7.694%	$139.2483	$139.25	$139.25	$139.20
7 purchase totals =	$887.49		$955.8725	$955.87	$955.90	$955.70