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	$96.26	4.280%	$100.3799	$100.38	$100.40	$100.40
Purchase #2	$229.81	13.211%	$260.1702	$260.17	$260.15	$260.20
Purchase #3	$179.66	3.832%	$186.5446	$186.54	$186.55	$186.50
Purchase #4	$111.91	13.790%	$127.3424	$127.34	$127.35	$127.30
Purchase #5	$17.50	5.618%	$18.4832	$18.48	$18.50	$18.50
Purchase #6	$94.88	10.334%	$104.6849	$104.68	$104.70	$104.70
Purchase #7	$173.97	3.307%	$179.7232	$179.72	$179.70	$179.70
7 purchase totals =	$903.99		$977.3284	$977.31	$977.35	$977.30