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	$30.39	4.202%	$31.667	$31.67	$31.65	$31.70
Purchase #2	$240.52	5.162%	$252.9356	$252.94	$252.95	$252.90
Purchase #3	$54.77	8.244%	$59.2852	$59.29	$59.30	$59.30
Purchase #4	$194.34	7.282%	$208.4918	$208.49	$208.50	$208.50
Purchase #5	$46.73	9.604%	$51.2179	$51.22	$51.20	$51.20
Purchase #6	$249.31	8.756%	$271.1396	$271.14	$271.15	$271.10
Purchase #7	$167.31	13.625%	$190.106	$190.11	$190.10	$190.10
7 purchase totals =	$983.37		$1,064.8431	$1,064.86	$1,064.85	$1,064.80