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	$159.39	4.221%	$166.1179	$166.12	$166.10	$166.10
Purchase #2	$165.83	8.456%	$179.8526	$179.85	$179.85	$179.90
Purchase #3	$20.42	5.151%	$21.4718	$21.47	$21.45	$21.50
Purchase #4	$99.47	4.123%	$103.5711	$103.57	$103.55	$103.60
Purchase #5	$242.66	13.472%	$275.3512	$275.35	$275.35	$275.40
Purchase #6	$195.67	12.809%	$220.7334	$220.73	$220.75	$220.70
Purchase #7	$154.72	12.349%	$173.8264	$173.83	$173.85	$173.80
7 purchase totals =	$1,038.16		$1,140.9244	$1,140.92	$1,140.90	$1,141.00