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	$43.90	11.256%	$48.8414	$48.84	$48.85	$48.80
Purchase #2	$47.58	3.719%	$49.3495	$49.35	$49.35	$49.30
Purchase #3	$118.25	4.372%	$123.4199	$123.42	$123.40	$123.40
Purchase #4	$166.87	13.198%	$188.8935	$188.89	$188.90	$188.90
Purchase #5	$171.64	11.380%	$191.1726	$191.17	$191.15	$191.20
Purchase #6	$190.28	3.770%	$197.4536	$197.45	$197.45	$197.50
Purchase #7	$37.39	7.535%	$40.2073	$40.21	$40.20	$40.20
7 purchase totals =	$775.91		$839.3378	$839.33	$839.30	$839.30