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	$6.85	13.180%	$7.7528	$7.75	$7.75	$7.80
Purchase #2	$117.95	10.354%	$130.1625	$130.16	$130.15	$130.20
Purchase #3	$73.91	6.365%	$78.6144	$78.61	$78.60	$78.60
Purchase #4	$200.29	12.707%	$225.7409	$225.74	$225.75	$225.70
Purchase #5	$211.85	11.717%	$236.6725	$236.67	$236.65	$236.70
Purchase #6	$249.89	13.118%	$282.6706	$282.67	$282.65	$282.70
Purchase #7	$141.66	3.663%	$146.849	$146.85	$146.85	$146.80
7 purchase totals =	$1,002.40		$1,108.4627	$1,108.45	$1,108.40	$1,108.50