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	$222.56	12.501%	$250.3822	$250.38	$250.40	$250.40
Purchase #2	$61.35	11.796%	$68.5868	$68.59	$68.60	$68.60
Purchase #3	$166.63	3.466%	$172.4054	$172.41	$172.40	$172.40
Purchase #4	$9.63	7.711%	$10.3726	$10.37	$10.35	$10.40
Purchase #5	$57.62	9.499%	$63.0933	$63.09	$63.10	$63.10
Purchase #6	$57.88	13.121%	$65.4744	$65.47	$65.45	$65.50
Purchase #7	$133.53	4.486%	$139.5202	$139.52	$139.50	$139.50
7 purchase totals =	$709.20		$769.8349	$769.83	$769.80	$769.90