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	$235.48	8.431%	$255.3333	$255.33	$255.35	$255.30
Purchase #2	$123.81	3.342%	$127.9477	$127.95	$127.95	$127.90
Purchase #3	$249.75	11.506%	$278.4862	$278.49	$278.50	$278.50
Purchase #4	$192.78	6.115%	$204.5685	$204.57	$204.55	$204.60
Purchase #5	$98.33	11.727%	$109.8612	$109.86	$109.85	$109.90
Purchase #6	$139.75	9.503%	$153.0304	$153.03	$153.05	$153.00
Purchase #7	$49.85	5.198%	$52.4412	$52.44	$52.45	$52.40
7 purchase totals =	$1,089.75		$1,181.6685	$1,181.67	$1,181.70	$1,181.60