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	$129.68	9.756%	$142.3316	$142.33	$142.35	$142.30
Purchase #2	$58.98	6.435%	$62.7754	$62.78	$62.80	$62.80
Purchase #3	$74.95	6.810%	$80.0541	$80.05	$80.05	$80.10
Purchase #4	$243.54	5.764%	$257.5776	$257.58	$257.60	$257.60
Purchase #5	$129.86	10.578%	$143.5966	$143.60	$143.60	$143.60
Purchase #6	$52.67	12.181%	$59.0857	$59.09	$59.10	$59.10
Purchase #7	$52.85	12.406%	$59.4066	$59.41	$59.40	$59.40
7 purchase totals =	$742.53		$804.8276	$804.84	$804.90	$804.90