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	$17.85	5.407%	$18.8151	$18.82	$18.80	$18.80
Purchase #2	$112.73	13.441%	$127.882	$127.88	$127.90	$127.90
Purchase #3	$239.43	7.146%	$256.5397	$256.54	$256.55	$256.50
Purchase #4	$32.75	7.245%	$35.1227	$35.12	$35.10	$35.10
Purchase #5	$128.99	13.146%	$145.947	$145.95	$145.95	$145.90
Purchase #6	$59.65	9.695%	$65.4331	$65.43	$65.45	$65.40
Purchase #7	$60.56	4.658%	$63.3809	$63.38	$63.40	$63.40
7 purchase totals =	$651.96		$713.1205	$713.12	$713.15	$713.00