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	$9.58	13.479%	$10.8713	$10.87	$10.85	$10.90
Purchase #2	$194.98	5.372%	$205.4543	$205.45	$205.45	$205.50
Purchase #3	$92.37	9.480%	$101.1267	$101.13	$101.15	$101.10
Purchase #4	$98.81	13.179%	$111.8322	$111.83	$111.85	$111.80
Purchase #5	$74.32	5.675%	$78.5377	$78.54	$78.55	$78.50
Purchase #6	$167.35	5.248%	$176.1325	$176.13	$176.15	$176.10
Purchase #7	$55.84	7.121%	$59.8164	$59.82	$59.80	$59.80
7 purchase totals =	$693.25		$743.7711	$743.77	$743.80	$743.70