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	$95.87	4.166%	$99.8639	$99.86	$99.85	$99.90
Purchase #2	$155.76	8.168%	$168.4825	$168.48	$168.50	$168.50
Purchase #3	$75.86	12.312%	$85.1999	$85.20	$85.20	$85.20
Purchase #4	$98.71	10.581%	$109.1545	$109.15	$109.15	$109.20
Purchase #5	$24.52	5.842%	$25.9525	$25.95	$25.95	$26.00
Purchase #6	$158.75	5.467%	$167.4289	$167.43	$167.45	$167.40
Purchase #7	$192.41	9.175%	$210.0636	$210.06	$210.05	$210.10
7 purchase totals =	$801.88		$866.1458	$866.13	$866.15	$866.30