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	$35.49	9.473%	$38.852	$38.85	$38.85	$38.90
Purchase #2	$118.78	7.314%	$127.4676	$127.47	$127.45	$127.50
Purchase #3	$239.69	13.585%	$272.2519	$272.25	$272.25	$272.30
Purchase #4	$95.42	4.742%	$99.9448	$99.94	$99.95	$99.90
Purchase #5	$25.81	5.751%	$27.2943	$27.29	$27.30	$27.30
Purchase #6	$89.80	10.764%	$99.4661	$99.47	$99.45	$99.50
Purchase #7	$202.30	8.424%	$219.3418	$219.34	$219.35	$219.30
7 purchase totals =	$807.29		$884.6185	$884.61	$884.60	$884.70