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	$66.47	9.658%	$72.8897	$72.89	$72.90	$72.90
Purchase #2	$111.51	13.789%	$126.8861	$126.89	$126.90	$126.90
Purchase #3	$173.94	6.432%	$185.1278	$185.13	$185.15	$185.10
Purchase #4	$79.74	3.281%	$82.3563	$82.36	$82.35	$82.40
Purchase #5	$146.30	8.815%	$159.1963	$159.20	$159.20	$159.20
Purchase #6	$24.96	13.697%	$28.3788	$28.38	$28.40	$28.40
Purchase #7	$110.49	10.395%	$121.9754	$121.98	$122.00	$122.00
7 purchase totals =	$713.41		$776.8104	$776.83	$776.90	$776.90