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	$71.42	5.607%	$75.4245	$75.42	$75.40	$75.40
Purchase #2	$40.87	11.275%	$45.4781	$45.48	$45.50	$45.50
Purchase #3	$51.63	13.810%	$58.7601	$58.76	$58.75	$58.80
Purchase #4	$94.32	4.628%	$98.6851	$98.69	$98.70	$98.70
Purchase #5	$172.46	3.356%	$178.2478	$178.25	$178.25	$178.20
Purchase #6	$99.95	11.777%	$111.7211	$111.72	$111.70	$111.70
Purchase #7	$43.81	8.288%	$47.441	$47.44	$47.45	$47.40
7 purchase totals =	$574.46		$615.7577	$615.76	$615.75	$615.70