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	$33.45	10.449%	$36.9452	$36.95	$36.95	$36.90
Purchase #2	$18.87	12.160%	$21.1646	$21.16	$21.15	$21.20
Purchase #3	$109.59	4.598%	$114.6289	$114.63	$114.65	$114.60
Purchase #4	$139.98	6.341%	$148.8561	$148.86	$148.85	$148.90
Purchase #5	$86.43	4.598%	$90.4041	$90.40	$90.40	$90.40
Purchase #6	$144.45	12.584%	$162.6276	$162.63	$162.65	$162.60
Purchase #7	$243.58	7.747%	$262.4501	$262.45	$262.45	$262.50
7 purchase totals =	$776.35		$837.0766	$837.08	$837.10	$837.10