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	$247.42	6.490%	$263.4776	$263.48	$263.50	$263.50
Purchase #2	$65.44	8.242%	$70.8336	$70.83	$70.85	$70.80
Purchase #3	$15.76	7.572%	$16.9533	$16.95	$16.95	$17.00
Purchase #4	$55.90	6.636%	$59.6095	$59.61	$59.60	$59.60
Purchase #5	$35.77	5.707%	$37.8114	$37.81	$37.80	$37.80
Purchase #6	$10.97	8.309%	$11.8815	$11.88	$11.90	$11.90
Purchase #7	$166.93	11.749%	$186.5426	$186.54	$186.55	$186.50
7 purchase totals =	$598.19		$647.1095	$647.10	$647.15	$647.10