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	$90.59	7.680%	$97.5473	$97.55	$97.55	$97.50
Purchase #2	$136.53	11.188%	$151.805	$151.81	$151.80	$151.80
Purchase #3	$100.96	10.223%	$111.2811	$111.28	$111.30	$111.30
Purchase #4	$180.42	5.532%	$190.4008	$190.40	$190.40	$190.40
Purchase #5	$6.25	8.303%	$6.7689	$6.77	$6.75	$6.80
Purchase #6	$81.41	4.429%	$85.0156	$85.02	$85.00	$85.00
Purchase #7	$45.40	3.792%	$47.1216	$47.12	$47.10	$47.10
7 purchase totals =	$641.56		$689.9403	$689.95	$689.90	$689.90