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	$140.82	8.553%	$152.8643	$152.86	$152.85	$152.90
Purchase #2	$231.63	8.260%	$250.7626	$250.76	$250.75	$250.80
Purchase #3	$30.58	3.414%	$31.624	$31.62	$31.60	$31.60
Purchase #4	$174.41	9.345%	$190.7086	$190.71	$190.70	$190.70
Purchase #5	$29.81	6.276%	$31.6809	$31.68	$31.70	$31.70
Purchase #6	$97.27	8.239%	$105.2841	$105.28	$105.30	$105.30
Purchase #7	$60.71	11.246%	$67.5374	$67.54	$67.55	$67.50
7 purchase totals =	$765.23		$830.4619	$830.45	$830.45	$830.50