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	$69.55	13.470%	$78.9184	$78.92	$78.90	$78.90
Purchase #2	$187.55	5.265%	$197.4245	$197.42	$197.40	$197.40
Purchase #3	$38.72	4.293%	$40.3822	$40.38	$40.40	$40.40
Purchase #4	$223.52	9.236%	$244.1643	$244.16	$244.15	$244.20
Purchase #5	$107.73	11.827%	$120.4712	$120.47	$120.45	$120.50
Purchase #6	$93.95	5.755%	$99.3568	$99.36	$99.35	$99.40
Purchase #7	$169.61	6.354%	$180.387	$180.39	$180.40	$180.40
7 purchase totals =	$890.63		$961.1044	$961.10	$961.05	$961.20