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	$37.83	12.250%	$42.4642	$42.46	$42.45	$42.50
Purchase #2	$9.31	10.398%	$10.2781	$10.28	$10.30	$10.30
Purchase #3	$199.52	4.496%	$208.4904	$208.49	$208.50	$208.50
Purchase #4	$184.82	4.405%	$192.9613	$192.96	$192.95	$193.00
Purchase #5	$145.87	4.799%	$152.8703	$152.87	$152.85	$152.90
Purchase #6	$93.25	5.737%	$98.5998	$98.60	$98.60	$98.60
Purchase #7	$131.93	6.735%	$140.8155	$140.82	$140.80	$140.80
7 purchase totals =	$802.53		$846.4796	$846.48	$846.45	$846.60