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	$123.76	12.496%	$139.225	$139.23	$139.25	$139.20
Purchase #2	$49.92	10.488%	$55.1556	$55.16	$55.15	$55.20
Purchase #3	$157.67	10.874%	$174.815	$174.82	$174.80	$174.80
Purchase #4	$118.72	4.416%	$123.9627	$123.96	$123.95	$124.00
Purchase #5	$132.84	8.275%	$143.8325	$143.83	$143.85	$143.80
Purchase #6	$130.97	12.608%	$147.4827	$147.48	$147.50	$147.50
Purchase #7	$87.26	3.400%	$90.2268	$90.23	$90.25	$90.20
7 purchase totals =	$801.14		$874.7003	$874.71	$874.75	$874.70