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	$39.80	5.650%	$42.0487	$42.05	$42.05	$42.00
Purchase #2	$123.96	4.324%	$129.32	$129.32	$129.30	$129.30
Purchase #3	$55.69	12.861%	$62.8523	$62.85	$62.85	$62.90
Purchase #4	$109.47	8.163%	$118.406	$118.41	$118.40	$118.40
Purchase #5	$99.67	12.531%	$112.1596	$112.16	$112.15	$112.20
Purchase #6	$141.64	8.353%	$153.4712	$153.47	$153.45	$153.50
Purchase #7	$246.29	3.480%	$254.8609	$254.86	$254.85	$254.90
7 purchase totals =	$816.52		$873.1187	$873.12	$873.05	$873.20