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	$28.25	4.188%	$29.4331	$29.43	$29.45	$29.40
Purchase #2	$151.78	10.370%	$167.5196	$167.52	$167.50	$167.50
Purchase #3	$71.85	11.520%	$80.1271	$80.13	$80.15	$80.10
Purchase #4	$116.41	9.412%	$127.3665	$127.37	$127.35	$127.40
Purchase #5	$94.92	11.287%	$105.6336	$105.63	$105.65	$105.60
Purchase #6	$31.52	11.121%	$35.0253	$35.03	$35.05	$35.00
Purchase #7	$39.31	6.362%	$41.8109	$41.81	$41.80	$41.80
7 purchase totals =	$534.04		$586.9161	$586.92	$586.95	$586.80