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	$150.48	9.607%	$164.9366	$164.94	$164.95	$164.90
Purchase #2	$94.48	6.419%	$100.5447	$100.54	$100.55	$100.50
Purchase #3	$129.34	13.873%	$147.2833	$147.28	$147.30	$147.30
Purchase #4	$18.72	12.293%	$21.0212	$21.02	$21.00	$21.00
Purchase #5	$184.78	11.279%	$205.6213	$205.62	$205.60	$205.60
Purchase #6	$27.79	11.242%	$30.9142	$30.91	$30.90	$30.90
Purchase #7	$242.70	13.782%	$276.1489	$276.15	$276.15	$276.10
7 purchase totals =	$848.29		$946.4702	$946.46	$946.45	$946.30