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	$51.69	7.339%	$55.4835	$55.48	$55.50	$55.50
Purchase #2	$183.91	6.771%	$196.3625	$196.36	$196.35	$196.40
Purchase #3	$190.56	12.543%	$214.4619	$214.46	$214.45	$214.50
Purchase #4	$71.77	11.391%	$79.9453	$79.95	$79.95	$79.90
Purchase #5	$138.41	6.515%	$147.4274	$147.43	$147.45	$147.40
Purchase #6	$243.84	4.712%	$255.3297	$255.33	$255.35	$255.30
Purchase #7	$157.99	9.248%	$172.6009	$172.60	$172.60	$172.60
7 purchase totals =	$1,038.17		$1,121.6112	$1,121.61	$1,121.65	$1,121.60