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	$26.35	10.329%	$29.0717	$29.07	$29.05	$29.10
Purchase #2	$176.48	11.469%	$196.7205	$196.72	$196.70	$196.70
Purchase #3	$65.98	8.690%	$71.7137	$71.71	$71.70	$71.70
Purchase #4	$118.64	5.418%	$125.0679	$125.07	$125.05	$125.10
Purchase #5	$56.42	5.462%	$59.5017	$59.50	$59.50	$59.50
Purchase #6	$199.84	5.648%	$211.127	$211.13	$211.15	$211.10
Purchase #7	$163.50	10.795%	$181.1498	$181.15	$181.15	$181.10
7 purchase totals =	$807.21		$874.3523	$874.35	$874.30	$874.30