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	$137.46	11.538%	$153.3201	$153.32	$153.30	$153.30
Purchase #2	$98.37	7.218%	$105.4703	$105.47	$105.45	$105.50
Purchase #3	$196.81	11.870%	$220.1713	$220.17	$220.15	$220.20
Purchase #4	$167.94	4.732%	$175.8869	$175.89	$175.90	$175.90
Purchase #5	$144.84	4.294%	$151.0594	$151.06	$151.05	$151.10
Purchase #6	$49.51	11.664%	$55.2848	$55.28	$55.30	$55.30
Purchase #7	$47.77	7.250%	$51.2333	$51.23	$51.25	$51.20
7 purchase totals =	$842.70		$912.4261	$912.42	$912.40	$912.50