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	$33.69	13.704%	$38.3069	$38.31	$38.30	$38.30
Purchase #2	$130.49	10.719%	$144.4772	$144.48	$144.50	$144.50
Purchase #3	$113.54	12.216%	$127.41	$127.41	$127.40	$127.40
Purchase #4	$190.78	9.685%	$209.257	$209.26	$209.25	$209.30
Purchase #5	$96.61	8.274%	$104.6035	$104.60	$104.60	$104.60
Purchase #6	$109.47	3.679%	$113.4974	$113.50	$113.50	$113.50
Purchase #7	$46.78	13.539%	$53.1135	$53.11	$53.10	$53.10
7 purchase totals =	$721.36		$790.6655	$790.67	$790.65	$790.70