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	$77.53	3.464%	$80.2156	$80.22	$80.20	$80.20
Purchase #2	$123.69	7.479%	$132.9408	$132.94	$132.95	$132.90
Purchase #3	$87.66	13.463%	$99.4617	$99.46	$99.45	$99.50
Purchase #4	$92.25	4.663%	$96.5516	$96.55	$96.55	$96.60
Purchase #5	$92.37	8.810%	$100.5078	$100.51	$100.50	$100.50
Purchase #6	$73.91	3.194%	$76.2707	$76.27	$76.25	$76.30
Purchase #7	$27.63	10.870%	$30.6334	$30.63	$30.65	$30.60
7 purchase totals =	$575.04		$616.5816	$616.58	$616.55	$616.60