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	$79.60	13.222%	$90.1247	$90.12	$90.10	$90.10
Purchase #2	$105.26	6.113%	$111.6945	$111.69	$111.70	$111.70
Purchase #3	$22.52	10.392%	$24.8603	$24.86	$24.85	$24.90
Purchase #4	$171.84	4.586%	$179.7206	$179.72	$179.70	$179.70
Purchase #5	$17.27	9.359%	$18.8863	$18.89	$18.90	$18.90
Purchase #6	$213.98	3.510%	$221.4907	$221.49	$221.50	$221.50
Purchase #7	$58.56	10.102%	$64.4757	$64.48	$64.50	$64.50
7 purchase totals =	$669.03		$711.2528	$711.25	$711.25	$711.30