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	$18.80	12.305%	$21.1133	$21.11	$21.10	$21.10
Purchase #2	$76.97	12.584%	$86.6559	$86.66	$86.65	$86.70
Purchase #3	$55.94	6.858%	$59.7764	$59.78	$59.80	$59.80
Purchase #4	$25.28	5.631%	$26.7035	$26.70	$26.70	$26.70
Purchase #5	$226.90	6.178%	$240.9179	$240.92	$240.90	$240.90
Purchase #6	$84.70	6.338%	$90.0683	$90.07	$90.05	$90.10
Purchase #7	$37.91	7.773%	$40.8567	$40.86	$40.85	$40.90
7 purchase totals =	$526.50		$566.0920	$566.10	$566.05	$566.20