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	$59.87	5.722%	$63.2958	$63.30	$63.30	$63.30
Purchase #2	$80.93	7.635%	$87.109	$87.11	$87.10	$87.10
Purchase #3	$138.27	11.689%	$154.4324	$154.43	$154.45	$154.40
Purchase #4	$120.75	6.195%	$128.2305	$128.23	$128.25	$128.20
Purchase #5	$29.34	10.623%	$32.4568	$32.46	$32.45	$32.50
Purchase #6	$199.80	11.314%	$222.4054	$222.41	$222.40	$222.40
Purchase #7	$162.35	12.491%	$182.6291	$182.63	$182.65	$182.60
7 purchase totals =	$791.31		$870.5590	$870.57	$870.60	$870.50