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	$39.52	3.395%	$40.8617	$40.86	$40.85	$40.90
Purchase #2	$141.87	10.271%	$156.4415	$156.44	$156.45	$156.40
Purchase #3	$118.33	8.446%	$128.3242	$128.32	$128.30	$128.30
Purchase #4	$5.76	4.846%	$6.0391	$6.04	$6.05	$6.00
Purchase #5	$165.67	7.244%	$177.6711	$177.67	$177.65	$177.70
Purchase #6	$55.33	4.626%	$57.8896	$57.89	$57.90	$57.90
Purchase #7	$126.97	3.402%	$131.2895	$131.29	$131.30	$131.30
7 purchase totals =	$653.45		$698.5167	$698.51	$698.50	$698.50