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	$124.85	9.505%	$136.717	$136.72	$136.70	$136.70
Purchase #2	$5.85	10.331%	$6.4544	$6.45	$6.45	$6.50
Purchase #3	$29.43	10.693%	$32.5769	$32.58	$32.60	$32.60
Purchase #4	$152.77	13.275%	$173.0502	$173.05	$173.05	$173.10
Purchase #5	$86.98	10.631%	$96.2268	$96.23	$96.25	$96.20
Purchase #6	$100.61	12.595%	$113.2818	$113.28	$113.30	$113.30
Purchase #7	$49.83	12.310%	$55.9641	$55.96	$55.95	$56.00
7 purchase totals =	$550.32		$614.2712	$614.27	$614.30	$614.40