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	$57.42	4.340%	$59.912	$59.91	$59.90	$59.90
Purchase #2	$79.54	5.268%	$83.7302	$83.73	$83.75	$83.70
Purchase #3	$19.65	3.115%	$20.2621	$20.26	$20.25	$20.30
Purchase #4	$124.37	5.477%	$131.1817	$131.18	$131.20	$131.20
Purchase #5	$57.94	3.700%	$60.0838	$60.08	$60.10	$60.10
Purchase #6	$110.38	5.458%	$116.4045	$116.40	$116.40	$116.40
Purchase #7	$228.49	4.726%	$239.2884	$239.29	$239.30	$239.30
7 purchase totals =	$677.79		$710.8627	$710.85	$710.90	$710.90