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	$114.69	5.109%	$120.5495	$120.55	$120.55	$120.50
Purchase #2	$160.65	8.109%	$173.6771	$173.68	$173.70	$173.70
Purchase #3	$237.35	13.272%	$268.8511	$268.85	$268.85	$268.90
Purchase #4	$57.54	11.564%	$64.1939	$64.19	$64.20	$64.20
Purchase #5	$30.82	5.488%	$32.5114	$32.51	$32.50	$32.50
Purchase #6	$224.81	13.546%	$255.2628	$255.26	$255.25	$255.30
Purchase #7	$45.83	3.646%	$47.501	$47.50	$47.50	$47.50
7 purchase totals =	$871.69		$962.5468	$962.54	$962.55	$962.60