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	$229.58	10.796%	$254.3655	$254.37	$254.35	$254.40
Purchase #2	$179.50	4.743%	$188.0137	$188.01	$188.00	$188.00
Purchase #3	$112.70	13.464%	$127.8739	$127.87	$127.85	$127.90
Purchase #4	$217.28	12.561%	$244.5725	$244.57	$244.55	$244.60
Purchase #5	$130.54	4.213%	$136.0397	$136.04	$136.05	$136.00
Purchase #6	$183.61	9.211%	$200.5223	$200.52	$200.50	$200.50
Purchase #7	$63.38	11.833%	$70.8798	$70.88	$70.90	$70.90
7 purchase totals =	$1,116.59		$1,222.2674	$1,222.26	$1,222.20	$1,222.30