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	$91.54	10.262%	$100.9338	$100.93	$100.95	$100.90
Purchase #2	$32.70	5.160%	$34.3873	$34.39	$34.40	$34.40
Purchase #3	$159.59	6.679%	$170.249	$170.25	$170.25	$170.20
Purchase #4	$203.77	7.830%	$219.7252	$219.73	$219.75	$219.70
Purchase #5	$5.90	12.353%	$6.6288	$6.63	$6.65	$6.60
Purchase #6	$200.59	11.585%	$223.8284	$223.83	$223.85	$223.80
Purchase #7	$227.81	4.800%	$238.7449	$238.74	$238.75	$238.70
7 purchase totals =	$921.90		$994.4974	$994.50	$994.60	$994.30