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	$99.96	11.557%	$111.5124	$111.51	$111.50	$111.50
Purchase #2	$9.53	4.615%	$9.9698	$9.97	$9.95	$10.00
Purchase #3	$220.58	13.543%	$250.4531	$250.45	$250.45	$250.50
Purchase #4	$50.38	8.643%	$54.7343	$54.73	$54.75	$54.70
Purchase #5	$151.56	7.139%	$162.3799	$162.38	$162.40	$162.40
Purchase #6	$145.90	4.154%	$151.9607	$151.96	$151.95	$152.00
Purchase #7	$78.60	13.374%	$89.112	$89.11	$89.10	$89.10
7 purchase totals =	$756.51		$830.1222	$830.11	$830.10	$830.20