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	$18.78	7.304%	$20.1517	$20.15	$20.15	$20.20
Purchase #2	$153.72	8.263%	$166.4219	$166.42	$166.40	$166.40
Purchase #3	$125.65	11.731%	$140.39	$140.39	$140.40	$140.40
Purchase #4	$122.82	3.663%	$127.3189	$127.32	$127.30	$127.30
Purchase #5	$68.53	12.608%	$77.1703	$77.17	$77.15	$77.20
Purchase #6	$28.89	11.618%	$32.2464	$32.25	$32.25	$32.20
Purchase #7	$35.36	11.389%	$39.3872	$39.39	$39.40	$39.40
7 purchase totals =	$553.75		$603.0864	$603.09	$603.05	$603.10