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	$158.34	3.818%	$164.3854	$164.39	$164.40	$164.40
Purchase #2	$22.61	10.585%	$25.0033	$25.00	$25.00	$25.00
Purchase #3	$145.51	10.314%	$160.5179	$160.52	$160.50	$160.50
Purchase #4	$89.62	10.495%	$99.0256	$99.03	$99.05	$99.00
Purchase #5	$39.80	11.134%	$44.2313	$44.23	$44.25	$44.20
Purchase #6	$28.32	9.523%	$31.0169	$31.02	$31.00	$31.00
Purchase #7	$60.71	11.704%	$67.8155	$67.82	$67.80	$67.80
7 purchase totals =	$544.91		$591.9959	$592.01	$592.00	$591.90