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	$21.75	11.538%	$24.2595	$24.26	$24.25	$24.30
Purchase #2	$38.78	9.276%	$42.3772	$42.38	$42.40	$42.40
Purchase #3	$46.86	7.542%	$50.3942	$50.39	$50.40	$50.40
Purchase #4	$10.61	9.434%	$11.6109	$11.61	$11.60	$11.60
Purchase #5	$34.83	8.223%	$37.6941	$37.69	$37.70	$37.70
Purchase #6	$69.29	5.519%	$73.1141	$73.11	$73.10	$73.10
Purchase #7	$235.96	3.538%	$244.3083	$244.31	$244.30	$244.30
7 purchase totals =	$458.08		$483.7583	$483.75	$483.75	$483.80