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	$59.95	10.833%	$66.4444	$66.44	$66.45	$66.40
Purchase #2	$206.96	7.644%	$222.78	$222.78	$222.80	$222.80
Purchase #3	$56.87	8.629%	$61.7773	$61.78	$61.80	$61.80
Purchase #4	$168.25	9.534%	$184.291	$184.29	$184.30	$184.30
Purchase #5	$167.76	6.794%	$179.1576	$179.16	$179.15	$179.20
Purchase #6	$60.92	7.340%	$65.3915	$65.39	$65.40	$65.40
Purchase #7	$139.91	7.418%	$150.2885	$150.29	$150.30	$150.30
7 purchase totals =	$860.62		$930.1303	$930.13	$930.20	$930.20