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	$82.71	7.735%	$89.1076	$89.11	$89.10	$89.10
Purchase #2	$248.49	13.238%	$281.3851	$281.39	$281.40	$281.40
Purchase #3	$117.78	7.306%	$126.385	$126.39	$126.40	$126.40
Purchase #4	$22.47	10.116%	$24.7431	$24.74	$24.75	$24.70
Purchase #5	$105.32	5.663%	$111.2843	$111.28	$111.30	$111.30
Purchase #6	$23.33	7.658%	$25.1166	$25.12	$25.10	$25.10
Purchase #7	$216.40	13.168%	$244.8956	$244.90	$244.90	$244.90
7 purchase totals =	$816.50		$902.9173	$902.93	$902.95	$902.90