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	$205.32	6.269%	$218.1915	$218.19	$218.20	$218.20
Purchase #2	$45.84	3.173%	$47.2945	$47.29	$47.30	$47.30
Purchase #3	$116.60	5.694%	$123.2392	$123.24	$123.25	$123.20
Purchase #4	$169.46	6.686%	$180.7901	$180.79	$180.80	$180.80
Purchase #5	$117.59	11.595%	$131.2246	$131.22	$131.20	$131.20
Purchase #6	$130.78	6.335%	$139.0649	$139.06	$139.05	$139.10
Purchase #7	$92.73	3.165%	$95.6649	$95.66	$95.65	$95.70
7 purchase totals =	$878.32		$935.4697	$935.45	$935.45	$935.50