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	$43.66	4.117%	$45.4575	$45.46	$45.45	$45.50
Purchase #2	$237.52	9.161%	$259.2792	$259.28	$259.30	$259.30
Purchase #3	$242.50	9.716%	$266.0613	$266.06	$266.05	$266.10
Purchase #4	$55.50	10.834%	$61.5129	$61.51	$61.50	$61.50
Purchase #5	$139.26	12.694%	$156.9377	$156.94	$156.95	$156.90
Purchase #6	$142.81	12.759%	$161.0311	$161.03	$161.05	$161.00
Purchase #7	$22.87	11.401%	$25.4774	$25.48	$25.50	$25.50
7 purchase totals =	$884.12		$975.7571	$975.76	$975.80	$975.80