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	$12.79	7.445%	$13.7422	$13.74	$13.75	$13.70
Purchase #2	$130.69	8.333%	$141.5804	$141.58	$141.60	$141.60
Purchase #3	$184.76	8.731%	$200.8914	$200.89	$200.90	$200.90
Purchase #4	$24.64	13.407%	$27.9435	$27.94	$27.95	$27.90
Purchase #5	$85.45	10.177%	$94.1462	$94.15	$94.15	$94.10
Purchase #6	$183.93	6.745%	$196.3361	$196.34	$196.35	$196.30
Purchase #7	$44.40	8.519%	$48.1824	$48.18	$48.20	$48.20
7 purchase totals =	$666.66		$722.8222	$722.82	$722.90	$722.70