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	$37.40	13.663%	$42.51	$42.51	$42.50	$42.50
Purchase #2	$31.29	7.407%	$33.6077	$33.61	$33.60	$33.60
Purchase #3	$61.30	11.526%	$68.3654	$68.37	$68.35	$68.40
Purchase #4	$169.63	5.720%	$179.3328	$179.33	$179.35	$179.30
Purchase #5	$199.72	11.277%	$222.2424	$222.24	$222.25	$222.20
Purchase #6	$178.71	12.295%	$200.6824	$200.68	$200.70	$200.70
Purchase #7	$94.83	5.281%	$99.838	$99.84	$99.85	$99.80
7 purchase totals =	$772.88		$846.5787	$846.58	$846.60	$846.50