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	$37.86	12.631%	$42.6421	$42.64	$42.65	$42.60
Purchase #2	$10.54	12.796%	$11.8887	$11.89	$11.90	$11.90
Purchase #3	$82.42	10.551%	$91.1161	$91.12	$91.10	$91.10
Purchase #4	$182.54	7.268%	$195.807	$195.81	$195.80	$195.80
Purchase #5	$13.80	6.304%	$14.67	$14.67	$14.65	$14.70
Purchase #6	$143.46	5.364%	$151.1552	$151.16	$151.15	$151.20
Purchase #7	$53.41	8.862%	$58.1432	$58.14	$58.15	$58.10
7 purchase totals =	$524.03		$565.4223	$565.43	$565.40	$565.40