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	$87.58	3.711%	$90.8301	$90.83	$90.85	$90.80
Purchase #2	$45.74	10.643%	$50.6081	$50.61	$50.60	$50.60
Purchase #3	$157.29	6.469%	$167.4651	$167.47	$167.45	$167.50
Purchase #4	$28.50	13.598%	$32.3754	$32.38	$32.40	$32.40
Purchase #5	$111.78	3.639%	$115.8477	$115.85	$115.85	$115.80
Purchase #6	$73.70	4.359%	$76.9126	$76.91	$76.90	$76.90
Purchase #7	$74.59	10.585%	$82.4854	$82.49	$82.50	$82.50
7 purchase totals =	$579.18		$616.5244	$616.54	$616.55	$616.50