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	$35.36	10.740%	$39.1577	$39.16	$39.15	$39.20
Purchase #2	$129.47	13.456%	$146.8915	$146.89	$146.90	$146.90
Purchase #3	$182.90	13.625%	$207.8201	$207.82	$207.80	$207.80
Purchase #4	$123.28	6.386%	$131.1527	$131.15	$131.15	$131.20
Purchase #5	$99.25	4.702%	$103.9167	$103.92	$103.90	$103.90
Purchase #6	$142.83	10.216%	$157.4215	$157.42	$157.40	$157.40
Purchase #7	$50.98	6.174%	$54.1275	$54.13	$54.15	$54.10
7 purchase totals =	$764.07		$840.4877	$840.49	$840.45	$840.50