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	$11.62	13.364%	$13.1729	$13.17	$13.15	$13.20
Purchase #2	$194.34	4.709%	$203.4915	$203.49	$203.50	$203.50
Purchase #3	$24.83	3.437%	$25.6834	$25.68	$25.70	$25.70
Purchase #4	$33.94	9.205%	$37.0642	$37.06	$37.05	$37.10
Purchase #5	$89.71	11.540%	$100.0625	$100.06	$100.05	$100.10
Purchase #6	$171.30	8.142%	$185.2472	$185.25	$185.25	$185.20
Purchase #7	$239.35	10.375%	$264.1826	$264.18	$264.20	$264.20
7 purchase totals =	$765.09		$828.9043	$828.89	$828.90	$829.00