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	$249.30	6.430%	$265.33	$265.33	$265.35	$265.30
Purchase #2	$131.76	3.796%	$136.7616	$136.76	$136.75	$136.80
Purchase #3	$179.98	4.593%	$188.2465	$188.25	$188.25	$188.20
Purchase #4	$101.93	9.185%	$111.2923	$111.29	$111.30	$111.30
Purchase #5	$42.65	13.288%	$48.3173	$48.32	$48.30	$48.30
Purchase #6	$13.42	5.556%	$14.1656	$14.17	$14.15	$14.20
Purchase #7	$67.47	3.230%	$69.6493	$69.65	$69.65	$69.60
7 purchase totals =	$786.51		$833.7626	$833.77	$833.75	$833.70