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	$138.73	11.206%	$154.2761	$154.28	$154.30	$154.30
Purchase #2	$124.93	5.596%	$131.9211	$131.92	$131.90	$131.90
Purchase #3	$110.93	11.693%	$123.901	$123.90	$123.90	$123.90
Purchase #4	$81.89	3.381%	$84.6587	$84.66	$84.65	$84.70
Purchase #5	$65.70	9.181%	$71.7319	$71.73	$71.75	$71.70
Purchase #6	$61.90	7.249%	$66.3871	$66.39	$66.40	$66.40
Purchase #7	$102.61	6.827%	$109.6152	$109.62	$109.60	$109.60
7 purchase totals =	$686.69		$742.4911	$742.50	$742.50	$742.50