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	$55.28	9.510%	$60.5371	$60.54	$60.55	$60.50
Purchase #2	$34.98	12.190%	$39.2441	$39.24	$39.25	$39.20
Purchase #3	$130.44	7.261%	$139.9112	$139.91	$139.90	$139.90
Purchase #4	$154.76	11.161%	$172.0328	$172.03	$172.05	$172.00
Purchase #5	$182.70	9.107%	$199.3385	$199.34	$199.35	$199.30
Purchase #6	$182.27	4.606%	$190.6654	$190.67	$190.65	$190.70
Purchase #7	$20.29	4.735%	$21.2507	$21.25	$21.25	$21.30
7 purchase totals =	$760.72		$822.9798	$822.98	$823.00	$822.90