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	$83.96	8.207%	$90.8506	$90.85	$90.85	$90.90
Purchase #2	$100.42	13.807%	$114.285	$114.29	$114.30	$114.30
Purchase #3	$66.89	4.711%	$70.0412	$70.04	$70.05	$70.00
Purchase #4	$216.45	12.792%	$244.1383	$244.14	$244.15	$244.10
Purchase #5	$36.29	12.231%	$40.7286	$40.73	$40.75	$40.70
Purchase #6	$240.27	8.521%	$260.7434	$260.74	$260.75	$260.70
Purchase #7	$49.32	12.379%	$55.4253	$55.43	$55.45	$55.40
7 purchase totals =	$793.60		$876.2124	$876.22	$876.30	$876.10