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	$38.82	6.253%	$41.2474	$41.25	$41.25	$41.20
Purchase #2	$220.48	11.549%	$245.9432	$245.94	$245.95	$245.90
Purchase #3	$238.25	6.625%	$254.0341	$254.03	$254.05	$254.00
Purchase #4	$16.32	10.847%	$18.0902	$18.09	$18.10	$18.10
Purchase #5	$63.80	12.651%	$71.8713	$71.87	$71.85	$71.90
Purchase #6	$22.84	12.169%	$25.6194	$25.62	$25.60	$25.60
Purchase #7	$115.91	10.111%	$127.6297	$127.63	$127.65	$127.60
7 purchase totals =	$716.42		$784.4353	$784.43	$784.45	$784.30