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	$49.92	10.573%	$55.198	$55.20	$55.20	$55.20
Purchase #2	$241.88	9.463%	$264.7691	$264.77	$264.75	$264.80
Purchase #3	$56.76	9.367%	$62.0767	$62.08	$62.10	$62.10
Purchase #4	$132.53	4.578%	$138.5972	$138.60	$138.60	$138.60
Purchase #5	$218.57	4.476%	$228.3532	$228.35	$228.35	$228.40
Purchase #6	$93.37	7.636%	$100.4997	$100.50	$100.50	$100.50
Purchase #7	$93.54	12.523%	$105.254	$105.25	$105.25	$105.30
7 purchase totals =	$886.57		$954.7479	$954.75	$954.75	$954.90