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	$10.86	12.231%	$12.1883	$12.19	$12.20	$12.20
Purchase #2	$140.45	8.812%	$152.8265	$152.83	$152.85	$152.80
Purchase #3	$235.75	6.242%	$250.4655	$250.47	$250.45	$250.50
Purchase #4	$100.97	7.281%	$108.3216	$108.32	$108.30	$108.30
Purchase #5	$102.25	9.263%	$111.7214	$111.72	$111.70	$111.70
Purchase #6	$24.42	13.682%	$27.7611	$27.76	$27.75	$27.80
Purchase #7	$243.28	9.162%	$265.5693	$265.57	$265.55	$265.60
7 purchase totals =	$857.98		$928.8537	$928.86	$928.80	$928.90