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	$187.63	12.199%	$210.519	$210.52	$210.50	$210.50
Purchase #2	$92.38	13.180%	$104.5557	$104.56	$104.55	$104.60
Purchase #3	$185.53	11.176%	$206.2648	$206.26	$206.25	$206.30
Purchase #4	$56.42	8.811%	$61.3912	$61.39	$61.40	$61.40
Purchase #5	$224.69	7.540%	$241.6316	$241.63	$241.65	$241.60
Purchase #6	$69.66	4.164%	$72.5606	$72.56	$72.55	$72.60
Purchase #7	$87.28	6.324%	$92.7996	$92.80	$92.80	$92.80
7 purchase totals =	$903.59		$989.7225	$989.72	$989.70	$989.80