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	$13.54	5.650%	$14.305	$14.31	$14.30	$14.30
Purchase #2	$43.53	13.499%	$49.4061	$49.41	$49.40	$49.40
Purchase #3	$99.37	3.636%	$102.9831	$102.98	$103.00	$103.00
Purchase #4	$138.45	12.664%	$155.9833	$155.98	$156.00	$156.00
Purchase #5	$53.74	7.625%	$57.8377	$57.84	$57.85	$57.80
Purchase #6	$191.61	4.688%	$200.5927	$200.59	$200.60	$200.60
Purchase #7	$80.30	6.870%	$85.8166	$85.82	$85.80	$85.80
7 purchase totals =	$620.54		$666.9245	$666.93	$666.95	$666.90