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	$113.36	12.712%	$127.7703	$127.77	$127.75	$127.80
Purchase #2	$122.62	4.336%	$127.9368	$127.94	$127.95	$127.90
Purchase #3	$123.65	5.125%	$129.9871	$129.99	$130.00	$130.00
Purchase #4	$75.31	4.827%	$78.9452	$78.95	$78.95	$78.90
Purchase #5	$49.35	5.522%	$52.0751	$52.08	$52.10	$52.10
Purchase #6	$55.46	11.524%	$61.8512	$61.85	$61.85	$61.90
Purchase #7	$5.56	13.631%	$6.3179	$6.32	$6.30	$6.30
7 purchase totals =	$545.31		$584.8836	$584.90	$584.90	$584.90