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	$131.54	13.128%	$148.8086	$148.81	$148.80	$148.80
Purchase #2	$80.50	13.563%	$91.4182	$91.42	$91.40	$91.40
Purchase #3	$96.74	6.858%	$103.3744	$103.37	$103.35	$103.40
Purchase #4	$229.29	4.270%	$239.0807	$239.08	$239.10	$239.10
Purchase #5	$106.34	4.747%	$111.388	$111.39	$111.40	$111.40
Purchase #6	$176.34	10.527%	$194.9033	$194.90	$194.90	$194.90
Purchase #7	$44.98	12.654%	$50.6718	$50.67	$50.65	$50.70
7 purchase totals =	$865.73		$939.6450	$939.64	$939.60	$939.70