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	$26.91	13.412%	$30.5192	$30.52	$30.50	$30.50
Purchase #2	$106.55	5.262%	$112.1567	$112.16	$112.15	$112.20
Purchase #3	$74.63	12.389%	$83.8759	$83.88	$83.90	$83.90
Purchase #4	$131.40	4.308%	$137.0607	$137.06	$137.05	$137.10
Purchase #5	$115.65	10.380%	$127.6545	$127.65	$127.65	$127.70
Purchase #6	$88.53	3.272%	$91.4267	$91.43	$91.45	$91.40
Purchase #7	$85.89	7.711%	$92.513	$92.51	$92.50	$92.50
7 purchase totals =	$629.56		$675.2067	$675.21	$675.20	$675.30