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	$120.90	3.211%	$124.7821	$124.78	$124.80	$124.80
Purchase #2	$102.48	10.861%	$113.6104	$113.61	$113.60	$113.60
Purchase #3	$58.26	13.342%	$66.033	$66.03	$66.05	$66.00
Purchase #4	$91.32	9.242%	$99.7598	$99.76	$99.75	$99.80
Purchase #5	$242.90	10.167%	$267.5956	$267.60	$267.60	$267.60
Purchase #6	$108.76	7.825%	$117.2705	$117.27	$117.25	$117.30
Purchase #7	$90.51	12.492%	$101.8165	$101.82	$101.80	$101.80
7 purchase totals =	$815.13		$890.8679	$890.87	$890.85	$890.90