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	$21.82	3.104%	$22.4973	$22.50	$22.50	$22.50
Purchase #2	$149.73	12.611%	$168.6125	$168.61	$168.60	$168.60
Purchase #3	$143.56	11.178%	$159.6071	$159.61	$159.60	$159.60
Purchase #4	$149.96	10.562%	$165.7988	$165.80	$165.80	$165.80
Purchase #5	$226.49	7.556%	$243.6036	$243.60	$243.60	$243.60
Purchase #6	$250.48	12.295%	$281.2765	$281.28	$281.30	$281.30
Purchase #7	$32.42	6.685%	$34.5873	$34.59	$34.60	$34.60
7 purchase totals =	$974.46		$1,075.9831	$1,075.99	$1,076.00	$1,076.00