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	$27.89	13.178%	$31.5653	$31.57	$31.55	$31.60
Purchase #2	$81.60	12.278%	$91.6188	$91.62	$91.60	$91.60
Purchase #3	$12.46	5.436%	$13.1373	$13.14	$13.15	$13.10
Purchase #4	$100.81	5.109%	$105.9604	$105.96	$105.95	$106.00
Purchase #5	$245.99	6.556%	$262.1171	$262.12	$262.10	$262.10
Purchase #6	$24.52	5.759%	$25.9321	$25.93	$25.95	$25.90
Purchase #7	$179.98	9.215%	$196.5652	$196.57	$196.55	$196.60
7 purchase totals =	$673.25		$726.8962	$726.91	$726.85	$726.90