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	$30.28	7.518%	$32.5565	$32.56	$32.55	$32.60
Purchase #2	$35.27	6.336%	$37.5047	$37.50	$37.50	$37.50
Purchase #3	$196.73	4.454%	$205.4924	$205.49	$205.50	$205.50
Purchase #4	$51.40	3.433%	$53.1646	$53.16	$53.15	$53.20
Purchase #5	$82.40	9.398%	$90.144	$90.14	$90.15	$90.10
Purchase #6	$42.80	12.844%	$48.2972	$48.30	$48.30	$48.30
Purchase #7	$109.84	11.297%	$122.2486	$122.25	$122.25	$122.20
7 purchase totals =	$548.72		$589.4080	$589.40	$589.40	$589.40