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	$39.45	11.298%	$43.9071	$43.91	$43.90	$43.90
Purchase #2	$168.28	6.712%	$179.575	$179.58	$179.60	$179.60
Purchase #3	$180.77	5.287%	$190.3273	$190.33	$190.35	$190.30
Purchase #4	$62.86	7.412%	$67.5192	$67.52	$67.50	$67.50
Purchase #5	$102.56	10.792%	$113.6283	$113.63	$113.65	$113.60
Purchase #6	$213.59	8.694%	$232.1595	$232.16	$232.15	$232.20
Purchase #7	$19.45	6.204%	$20.6567	$20.66	$20.65	$20.70
7 purchase totals =	$786.96		$847.7731	$847.79	$847.80	$847.80