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	$179.66	11.823%	$200.9012	$200.90	$200.90	$200.90
Purchase #2	$61.34	7.803%	$66.1264	$66.13	$66.15	$66.10
Purchase #3	$39.34	5.155%	$41.368	$41.37	$41.35	$41.40
Purchase #4	$87.65	3.788%	$90.9702	$90.97	$90.95	$91.00
Purchase #5	$104.90	8.499%	$113.8155	$113.82	$113.80	$113.80
Purchase #6	$116.96	13.516%	$132.7683	$132.77	$132.75	$132.80
Purchase #7	$152.87	13.411%	$173.3714	$173.37	$173.35	$173.40
7 purchase totals =	$742.72		$819.3210	$819.33	$819.25	$819.40