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	$183.30	3.861%	$190.3772	$190.38	$190.40	$190.40
Purchase #2	$55.50	8.328%	$60.122	$60.12	$60.10	$60.10
Purchase #3	$77.71	10.465%	$85.8424	$85.84	$85.85	$85.80
Purchase #4	$16.27	11.507%	$18.1422	$18.14	$18.15	$18.10
Purchase #5	$126.72	10.817%	$140.4273	$140.43	$140.45	$140.40
Purchase #6	$83.41	10.457%	$92.1322	$92.13	$92.15	$92.10
Purchase #7	$22.76	12.521%	$25.6098	$25.61	$25.60	$25.60
7 purchase totals =	$565.67		$612.6531	$612.65	$612.70	$612.50