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	$226.89	9.111%	$247.5619	$247.56	$247.55	$247.60
Purchase #2	$96.62	6.253%	$102.6616	$102.66	$102.65	$102.70
Purchase #3	$192.56	11.687%	$215.0645	$215.06	$215.05	$215.10
Purchase #4	$19.70	12.537%	$22.1698	$22.17	$22.15	$22.20
Purchase #5	$119.54	6.690%	$127.5372	$127.54	$127.55	$127.50
Purchase #6	$158.74	4.463%	$165.8246	$165.82	$165.80	$165.80
Purchase #7	$98.84	10.860%	$109.574	$109.57	$109.55	$109.60
7 purchase totals =	$912.89		$990.3936	$990.38	$990.30	$990.50