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	$211.96	10.761%	$234.769	$234.77	$234.75	$234.80
Purchase #2	$174.28	12.509%	$196.0807	$196.08	$196.10	$196.10
Purchase #3	$164.95	4.197%	$171.873	$171.87	$171.85	$171.90
Purchase #4	$16.48	8.573%	$17.8928	$17.89	$17.90	$17.90
Purchase #5	$223.67	4.390%	$233.4891	$233.49	$233.50	$233.50
Purchase #6	$59.35	5.578%	$62.6605	$62.66	$62.65	$62.70
Purchase #7	$5.62	7.341%	$6.0326	$6.03	$6.05	$6.00
7 purchase totals =	$856.31		$922.7977	$922.79	$922.80	$922.90