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	$183.40	3.329%	$189.5054	$189.51	$189.50	$189.50
Purchase #2	$108.52	8.654%	$117.9113	$117.91	$117.90	$117.90
Purchase #3	$78.90	9.437%	$86.3458	$86.35	$86.35	$86.30
Purchase #4	$154.59	11.342%	$172.1236	$172.12	$172.10	$172.10
Purchase #5	$11.65	9.649%	$12.7741	$12.77	$12.75	$12.80
Purchase #6	$79.54	13.796%	$90.5133	$90.51	$90.50	$90.50
Purchase #7	$90.39	6.316%	$96.099	$96.10	$96.10	$96.10
7 purchase totals =	$706.99		$765.2725	$765.27	$765.20	$765.20