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	$28.30	6.504%	$30.1406	$30.14	$30.15	$30.10
Purchase #2	$93.58	6.707%	$99.8564	$99.86	$99.85	$99.90
Purchase #3	$141.97	8.258%	$153.6939	$153.69	$153.70	$153.70
Purchase #4	$250.67	12.701%	$282.5076	$282.51	$282.50	$282.50
Purchase #5	$31.78	6.405%	$33.8155	$33.82	$33.80	$33.80
Purchase #6	$163.95	5.378%	$172.7672	$172.77	$172.75	$172.80
Purchase #7	$244.60	4.297%	$255.1105	$255.11	$255.10	$255.10
7 purchase totals =	$954.85		$1,027.8917	$1,027.90	$1,027.85	$1,027.90