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	$38.57	9.544%	$42.2511	$42.25	$42.25	$42.30
Purchase #2	$183.47	9.490%	$200.8813	$200.88	$200.90	$200.90
Purchase #3	$115.43	10.365%	$127.3943	$127.39	$127.40	$127.40
Purchase #4	$7.43	9.246%	$8.117	$8.12	$8.10	$8.10
Purchase #5	$16.37	11.487%	$18.2504	$18.25	$18.25	$18.30
Purchase #6	$105.83	9.546%	$115.9325	$115.93	$115.95	$115.90
Purchase #7	$7.99	7.784%	$8.6119	$8.61	$8.60	$8.60
7 purchase totals =	$475.09		$521.4385	$521.43	$521.45	$521.50