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	$138.89	5.178%	$146.0817	$146.08	$146.10	$146.10
Purchase #2	$166.93	8.661%	$181.3878	$181.39	$181.40	$181.40
Purchase #3	$154.44	8.741%	$167.9396	$167.94	$167.95	$167.90
Purchase #4	$81.34	11.710%	$90.8649	$90.86	$90.85	$90.90
Purchase #5	$228.34	12.314%	$256.4578	$256.46	$256.45	$256.50
Purchase #6	$197.97	10.760%	$219.2716	$219.27	$219.25	$219.30
Purchase #7	$80.82	12.304%	$90.7641	$90.76	$90.75	$90.80
7 purchase totals =	$1,048.73		$1,152.7675	$1,152.76	$1,152.75	$1,152.90