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	$45.42	8.170%	$49.1308	$49.13	$49.15	$49.10
Purchase #2	$223.65	13.681%	$254.2476	$254.25	$254.25	$254.20
Purchase #3	$18.87	9.178%	$20.6019	$20.60	$20.60	$20.60
Purchase #4	$30.80	7.845%	$33.2163	$33.22	$33.20	$33.20
Purchase #5	$239.83	6.664%	$255.8123	$255.81	$255.80	$255.80
Purchase #6	$53.52	7.452%	$57.5083	$57.51	$57.50	$57.50
Purchase #7	$170.46	11.342%	$189.7936	$189.79	$189.80	$189.80
7 purchase totals =	$782.55		$860.3108	$860.31	$860.30	$860.20