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	$34.58	8.349%	$37.4671	$37.47	$37.45	$37.50
Purchase #2	$145.98	13.212%	$165.2669	$165.27	$165.25	$165.30
Purchase #3	$30.94	13.143%	$35.0064	$35.01	$35.00	$35.00
Purchase #4	$17.92	12.467%	$20.1541	$20.15	$20.15	$20.20
Purchase #5	$67.83	7.104%	$72.6486	$72.65	$72.65	$72.60
Purchase #6	$75.40	3.567%	$78.0895	$78.09	$78.10	$78.10
Purchase #7	$250.73	4.742%	$262.6196	$262.62	$262.60	$262.60
7 purchase totals =	$623.38		$671.2522	$671.26	$671.20	$671.30