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	$231.78	10.299%	$255.651	$255.65	$255.65	$255.70
Purchase #2	$193.86	9.368%	$212.0208	$212.02	$212.00	$212.00
Purchase #3	$95.25	4.347%	$99.3905	$99.39	$99.40	$99.40
Purchase #4	$23.80	6.774%	$25.4122	$25.41	$25.40	$25.40
Purchase #5	$116.60	11.709%	$130.2527	$130.25	$130.25	$130.30
Purchase #6	$69.75	10.145%	$76.8261	$76.83	$76.85	$76.80
Purchase #7	$53.33	6.590%	$56.8444	$56.84	$56.85	$56.80
7 purchase totals =	$784.37		$856.3977	$856.39	$856.40	$856.40