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	$10.68	3.799%	$11.0857	$11.09	$11.10	$11.10
Purchase #2	$29.91	6.786%	$31.9397	$31.94	$31.95	$31.90
Purchase #3	$182.94	11.708%	$204.3586	$204.36	$204.35	$204.40
Purchase #4	$101.43	11.710%	$113.3075	$113.31	$113.30	$113.30
Purchase #5	$138.29	3.111%	$142.5922	$142.59	$142.60	$142.60
Purchase #6	$108.31	4.279%	$112.9446	$112.94	$112.95	$112.90
Purchase #7	$63.52	12.658%	$71.5604	$71.56	$71.55	$71.60
7 purchase totals =	$635.08		$687.7887	$687.79	$687.80	$687.80