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	$53.48	10.296%	$58.9863	$58.99	$59.00	$59.00
Purchase #2	$102.48	13.786%	$116.6079	$116.61	$116.60	$116.60
Purchase #3	$210.88	10.742%	$233.5327	$233.53	$233.55	$233.50
Purchase #4	$167.86	10.156%	$184.9079	$184.91	$184.90	$184.90
Purchase #5	$111.59	6.324%	$118.647	$118.65	$118.65	$118.60
Purchase #6	$99.85	5.152%	$104.9943	$104.99	$105.00	$105.00
Purchase #7	$56.93	11.222%	$63.3187	$63.32	$63.30	$63.30
7 purchase totals =	$803.07		$880.9948	$881.00	$881.00	$880.90