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	$93.80	10.702%	$103.8385	$103.84	$103.85	$103.80
Purchase #2	$49.69	13.742%	$56.5184	$56.52	$56.50	$56.50
Purchase #3	$112.77	5.424%	$118.8866	$118.89	$118.90	$118.90
Purchase #4	$186.45	7.352%	$200.1578	$200.16	$200.15	$200.20
Purchase #5	$53.88	6.387%	$57.3213	$57.32	$57.30	$57.30
Purchase #6	$152.79	12.777%	$172.312	$172.31	$172.30	$172.30
Purchase #7	$103.88	8.359%	$112.5633	$112.56	$112.55	$112.60
7 purchase totals =	$753.26		$821.5979	$821.60	$821.55	$821.60