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	$42.58	6.810%	$45.4797	$45.48	$45.50	$45.50
Purchase #2	$126.73	7.361%	$136.0586	$136.06	$136.05	$136.10
Purchase #3	$223.43	9.541%	$244.7475	$244.75	$244.75	$244.70
Purchase #4	$127.78	11.504%	$142.4798	$142.48	$142.50	$142.50
Purchase #5	$56.83	3.861%	$59.0242	$59.02	$59.00	$59.00
Purchase #6	$209.89	11.209%	$233.4166	$233.42	$233.40	$233.40
Purchase #7	$67.99	13.544%	$77.1986	$77.20	$77.20	$77.20
7 purchase totals =	$855.23		$938.4050	$938.41	$938.40	$938.40