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	$25.48	11.812%	$28.4897	$28.49	$28.50	$28.50
Purchase #2	$117.74	8.330%	$127.5477	$127.55	$127.55	$127.50
Purchase #3	$39.49	5.326%	$41.5932	$41.59	$41.60	$41.60
Purchase #4	$234.68	7.702%	$252.7551	$252.76	$252.75	$252.80
Purchase #5	$79.34	11.589%	$88.5347	$88.53	$88.55	$88.50
Purchase #6	$129.41	11.865%	$144.7645	$144.76	$144.75	$144.80
Purchase #7	$109.25	12.809%	$123.2438	$123.24	$123.25	$123.20
7 purchase totals =	$735.39		$806.9287	$806.92	$806.95	$806.90