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	$132.34	7.714%	$142.5487	$142.55	$142.55	$142.50
Purchase #2	$250.64	12.181%	$281.1705	$281.17	$281.15	$281.20
Purchase #3	$163.33	5.510%	$172.3295	$172.33	$172.35	$172.30
Purchase #4	$175.77	6.649%	$187.4569	$187.46	$187.45	$187.50
Purchase #5	$131.81	10.270%	$145.3469	$145.35	$145.35	$145.30
Purchase #6	$82.36	5.571%	$86.9483	$86.95	$86.95	$86.90
Purchase #7	$48.54	12.850%	$54.7774	$54.78	$54.80	$54.80
7 purchase totals =	$984.79		$1,070.5782	$1,070.59	$1,070.60	$1,070.50