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	$17.48	4.491%	$18.265	$18.27	$18.25	$18.30
Purchase #2	$190.56	6.250%	$202.47	$202.47	$202.45	$202.50
Purchase #3	$10.53	3.438%	$10.892	$10.89	$10.90	$10.90
Purchase #4	$184.35	8.310%	$199.6695	$199.67	$199.65	$199.70
Purchase #5	$89.37	3.676%	$92.6552	$92.66	$92.65	$92.70
Purchase #6	$25.82	7.872%	$27.8526	$27.85	$27.85	$27.90
Purchase #7	$105.78	5.311%	$111.398	$111.40	$111.40	$111.40
7 purchase totals =	$623.89		$663.2023	$663.21	$663.15	$663.40