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	$122.77	3.628%	$127.2241	$127.22	$127.20	$127.20
Purchase #2	$196.52	11.655%	$219.4244	$219.42	$219.40	$219.40
Purchase #3	$54.69	9.202%	$59.7226	$59.72	$59.70	$59.70
Purchase #4	$86.66	7.378%	$93.0538	$93.05	$93.05	$93.10
Purchase #5	$113.35	13.303%	$128.429	$128.43	$128.45	$128.40
Purchase #6	$135.74	4.378%	$141.6827	$141.68	$141.70	$141.70
Purchase #7	$80.57	10.325%	$88.8889	$88.89	$88.90	$88.90
7 purchase totals =	$790.30		$858.4255	$858.41	$858.40	$858.40