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	$53.81	10.211%	$59.3045	$59.30	$59.30	$59.30
Purchase #2	$169.57	10.607%	$187.5563	$187.56	$187.55	$187.60
Purchase #3	$42.43	5.133%	$44.6079	$44.61	$44.60	$44.60
Purchase #4	$143.45	4.497%	$149.9009	$149.90	$149.90	$149.90
Purchase #5	$79.25	5.673%	$83.7459	$83.75	$83.75	$83.70
Purchase #6	$42.43	4.851%	$44.4883	$44.49	$44.50	$44.50
Purchase #7	$10.53	9.497%	$11.53	$11.53	$11.55	$11.50
7 purchase totals =	$541.47		$581.1338	$581.14	$581.15	$581.10