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	$44.60	10.315%	$49.2005	$49.20	$49.20	$49.20
Purchase #2	$52.91	13.519%	$60.0629	$60.06	$60.05	$60.10
Purchase #3	$244.38	4.663%	$255.7754	$255.78	$255.80	$255.80
Purchase #4	$39.40	11.128%	$43.7844	$43.78	$43.80	$43.80
Purchase #5	$7.91	11.190%	$8.7951	$8.80	$8.80	$8.80
Purchase #6	$63.95	12.412%	$71.8875	$71.89	$71.90	$71.90
Purchase #7	$158.28	9.254%	$172.9272	$172.93	$172.95	$172.90
7 purchase totals =	$611.43		$662.4330	$662.44	$662.50	$662.50