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	$90.43	13.628%	$102.7538	$102.75	$102.75	$102.80
Purchase #2	$223.97	4.254%	$233.4977	$233.50	$233.50	$233.50
Purchase #3	$221.94	6.595%	$236.5769	$236.58	$236.60	$236.60
Purchase #4	$204.77	6.572%	$218.2275	$218.23	$218.25	$218.20
Purchase #5	$89.48	12.664%	$100.8117	$100.81	$100.80	$100.80
Purchase #6	$164.63	3.801%	$170.8876	$170.89	$170.90	$170.90
Purchase #7	$43.99	5.760%	$46.5238	$46.52	$46.50	$46.50
7 purchase totals =	$1,039.21		$1,109.2790	$1,109.28	$1,109.30	$1,109.30