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	$73.69	13.866%	$83.9079	$83.91	$83.90	$83.90
Purchase #2	$112.55	9.832%	$123.6159	$123.62	$123.60	$123.60
Purchase #3	$86.57	13.873%	$98.5799	$98.58	$98.60	$98.60
Purchase #4	$241.33	8.210%	$261.1432	$261.14	$261.15	$261.10
Purchase #5	$115.64	10.497%	$127.7787	$127.78	$127.80	$127.80
Purchase #6	$164.72	10.749%	$182.4258	$182.43	$182.45	$182.40
Purchase #7	$28.56	4.258%	$29.7761	$29.78	$29.80	$29.80
7 purchase totals =	$823.06		$907.2275	$907.24	$907.30	$907.20