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	$247.45	12.854%	$279.2572	$279.26	$279.25	$279.30
Purchase #2	$111.78	10.653%	$123.6879	$123.69	$123.70	$123.70
Purchase #3	$227.90	4.692%	$238.5931	$238.59	$238.60	$238.60
Purchase #4	$152.86	5.778%	$161.6923	$161.69	$161.70	$161.70
Purchase #5	$49.80	12.129%	$55.8402	$55.84	$55.85	$55.80
Purchase #6	$26.40	7.707%	$28.4346	$28.43	$28.45	$28.40
Purchase #7	$145.73	11.527%	$162.5283	$162.53	$162.55	$162.50
7 purchase totals =	$961.92		$1,050.0336	$1,050.03	$1,050.10	$1,050.00