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	$18.46	10.650%	$20.426	$20.43	$20.45	$20.40
Purchase #2	$24.70	3.282%	$25.5107	$25.51	$25.50	$25.50
Purchase #3	$81.52	10.363%	$89.9679	$89.97	$89.95	$90.00
Purchase #4	$109.40	12.238%	$122.7884	$122.79	$122.80	$122.80
Purchase #5	$64.64	6.113%	$68.5914	$68.59	$68.60	$68.60
Purchase #6	$218.45	4.320%	$227.887	$227.89	$227.90	$227.90
Purchase #7	$64.91	4.645%	$67.9251	$67.93	$67.95	$67.90
7 purchase totals =	$582.08		$623.0965	$623.11	$623.15	$623.10