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	$45.96	6.797%	$49.0839	$49.08	$49.10	$49.10
Purchase #2	$248.51	12.597%	$279.8148	$279.81	$279.80	$279.80
Purchase #3	$104.44	6.596%	$111.3289	$111.33	$111.35	$111.30
Purchase #4	$7.58	3.577%	$7.8511	$7.85	$7.85	$7.90
Purchase #5	$187.40	12.215%	$210.2909	$210.29	$210.30	$210.30
Purchase #6	$54.33	9.761%	$59.6332	$59.63	$59.65	$59.60
Purchase #7	$173.97	13.832%	$198.0335	$198.03	$198.05	$198.00
7 purchase totals =	$822.19		$916.0363	$916.02	$916.10	$916.00