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	$36.36	3.119%	$37.4941	$37.49	$37.50	$37.50
Purchase #2	$158.75	11.408%	$176.8602	$176.86	$176.85	$176.90
Purchase #3	$157.29	10.244%	$173.4028	$173.40	$173.40	$173.40
Purchase #4	$99.55	11.404%	$110.9027	$110.90	$110.90	$110.90
Purchase #5	$199.29	8.370%	$215.9706	$215.97	$215.95	$216.00
Purchase #6	$145.52	4.550%	$152.1412	$152.14	$152.15	$152.10
Purchase #7	$186.45	13.197%	$211.0558	$211.06	$211.05	$211.10
7 purchase totals =	$983.21		$1,077.8274	$1,077.82	$1,077.80	$1,077.90