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	$79.88	11.849%	$89.345	$89.35	$89.35	$89.30
Purchase #2	$124.58	13.713%	$141.6637	$141.66	$141.65	$141.70
Purchase #3	$43.42	6.486%	$46.2362	$46.24	$46.25	$46.20
Purchase #4	$58.25	9.291%	$63.662	$63.66	$63.65	$63.70
Purchase #5	$114.97	7.312%	$123.3766	$123.38	$123.40	$123.40
Purchase #6	$105.65	13.508%	$119.9212	$119.92	$119.90	$119.90
Purchase #7	$185.47	12.784%	$209.1805	$209.18	$209.20	$209.20
7 purchase totals =	$712.22		$793.3852	$793.39	$793.40	$793.40