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	$107.68	6.521%	$114.7018	$114.70	$114.70	$114.70
Purchase #2	$145.58	7.745%	$156.8552	$156.86	$156.85	$156.90
Purchase #3	$238.39	6.196%	$253.1606	$253.16	$253.15	$253.20
Purchase #4	$34.41	4.146%	$35.8366	$35.84	$35.85	$35.80
Purchase #5	$37.55	4.363%	$39.1883	$39.19	$39.20	$39.20
Purchase #6	$107.85	4.142%	$112.3171	$112.32	$112.30	$112.30
Purchase #7	$77.84	10.289%	$85.849	$85.85	$85.85	$85.80
7 purchase totals =	$749.30		$797.9086	$797.92	$797.90	$797.90