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	$161.29	4.421%	$168.4206	$168.42	$168.40	$168.40
Purchase #2	$195.74	13.605%	$222.3704	$222.37	$222.35	$222.40
Purchase #3	$152.62	6.486%	$162.5189	$162.52	$162.50	$162.50
Purchase #4	$47.68	10.338%	$52.6092	$52.61	$52.60	$52.60
Purchase #5	$10.89	10.764%	$12.0622	$12.06	$12.05	$12.10
Purchase #6	$70.78	5.842%	$74.915	$74.92	$74.90	$74.90
Purchase #7	$122.97	4.789%	$128.859	$128.86	$128.85	$128.90
7 purchase totals =	$761.97		$821.7553	$821.76	$821.65	$821.80