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	$156.36	6.252%	$166.1356	$166.14	$166.15	$166.10
Purchase #2	$87.49	9.525%	$95.8234	$95.82	$95.80	$95.80
Purchase #3	$44.92	10.680%	$49.7175	$49.72	$49.70	$49.70
Purchase #4	$59.71	8.538%	$64.808	$64.81	$64.80	$64.80
Purchase #5	$211.89	12.519%	$238.4165	$238.42	$238.40	$238.40
Purchase #6	$131.61	5.512%	$138.8643	$138.86	$138.85	$138.90
Purchase #7	$215.80	3.716%	$223.8191	$223.82	$223.80	$223.80
7 purchase totals =	$907.78		$977.5844	$977.59	$977.50	$977.50