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	$250.38	11.595%	$279.4116	$279.41	$279.40	$279.40
Purchase #2	$68.64	3.216%	$70.8475	$70.85	$70.85	$70.80
Purchase #3	$142.25	6.188%	$151.0524	$151.05	$151.05	$151.10
Purchase #4	$212.25	6.166%	$225.3373	$225.34	$225.35	$225.30
Purchase #5	$145.60	11.383%	$162.1736	$162.17	$162.15	$162.20
Purchase #6	$11.72	5.735%	$12.3921	$12.39	$12.40	$12.40
Purchase #7	$100.90	9.265%	$110.2484	$110.25	$110.25	$110.20
7 purchase totals =	$931.74		$1,011.4629	$1,011.46	$1,011.45	$1,011.40