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	$16.39	11.303%	$18.2426	$18.24	$18.25	$18.20
Purchase #2	$49.93	11.785%	$55.8143	$55.81	$55.80	$55.80
Purchase #3	$152.59	5.411%	$160.8466	$160.85	$160.85	$160.80
Purchase #4	$184.69	8.656%	$200.6768	$200.68	$200.70	$200.70
Purchase #5	$25.41	12.557%	$28.6007	$28.60	$28.60	$28.60
Purchase #6	$181.62	9.663%	$199.1699	$199.17	$199.15	$199.20
Purchase #7	$212.49	4.733%	$222.5472	$222.55	$222.55	$222.50
7 purchase totals =	$823.12		$885.8981	$885.90	$885.90	$885.80