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	$46.50	12.124%	$52.1377	$52.14	$52.15	$52.10
Purchase #2	$199.32	8.450%	$216.1625	$216.16	$216.15	$216.20
Purchase #3	$39.43	3.587%	$40.8444	$40.84	$40.85	$40.80
Purchase #4	$28.84	10.439%	$31.8506	$31.85	$31.85	$31.90
Purchase #5	$184.52	13.723%	$209.8417	$209.84	$209.85	$209.80
Purchase #6	$152.85	13.459%	$173.4221	$173.42	$173.40	$173.40
Purchase #7	$112.25	11.279%	$124.9107	$124.91	$124.90	$124.90
7 purchase totals =	$763.71		$849.1697	$849.16	$849.15	$849.10