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	$245.88	10.672%	$272.1203	$272.12	$272.10	$272.10
Purchase #2	$164.55	7.291%	$176.5473	$176.55	$176.55	$176.50
Purchase #3	$168.89	12.844%	$190.5822	$190.58	$190.60	$190.60
Purchase #4	$98.89	12.244%	$110.9981	$111.00	$111.00	$111.00
Purchase #5	$226.76	10.187%	$249.86	$249.86	$249.85	$249.90
Purchase #6	$206.68	10.480%	$228.3401	$228.34	$228.35	$228.30
Purchase #7	$173.69	13.301%	$196.7925	$196.79	$196.80	$196.80
7 purchase totals =	$1,285.34		$1,425.2405	$1,425.24	$1,425.25	$1,425.20