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	$23.31	7.352%	$25.0238	$25.02	$25.00	$25.00
Purchase #2	$9.70	11.501%	$10.8156	$10.82	$10.80	$10.80
Purchase #3	$158.52	12.470%	$178.2874	$178.29	$178.30	$178.30
Purchase #4	$90.96	10.663%	$100.6591	$100.66	$100.65	$100.70
Purchase #5	$209.90	12.367%	$235.8583	$235.86	$235.85	$235.90
Purchase #6	$82.50	8.195%	$89.2609	$89.26	$89.25	$89.30
Purchase #7	$207.34	5.802%	$219.3699	$219.37	$219.35	$219.40
7 purchase totals =	$782.23		$859.2750	$859.28	$859.20	$859.40