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	$14.82	3.308%	$15.3102	$15.31	$15.30	$15.30
Purchase #2	$143.71	5.361%	$151.4143	$151.41	$151.40	$151.40
Purchase #3	$20.51	11.406%	$22.8494	$22.85	$22.85	$22.80
Purchase #4	$210.67	12.777%	$237.5873	$237.59	$237.60	$237.60
Purchase #5	$77.47	6.548%	$82.5427	$82.54	$82.55	$82.50
Purchase #6	$235.32	13.285%	$266.5823	$266.58	$266.60	$266.60
Purchase #7	$206.73	11.226%	$229.9375	$229.94	$229.95	$229.90
7 purchase totals =	$909.23		$1,006.2237	$1,006.22	$1,006.25	$1,006.10