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	$106.85	5.583%	$112.8154	$112.82	$112.80	$112.80
Purchase #2	$237.53	9.646%	$260.4421	$260.44	$260.45	$260.40
Purchase #3	$121.34	13.225%	$137.3872	$137.39	$137.40	$137.40
Purchase #4	$82.88	9.602%	$90.8381	$90.84	$90.85	$90.80
Purchase #5	$63.54	9.112%	$69.3298	$69.33	$69.35	$69.30
Purchase #6	$46.94	4.154%	$48.8899	$48.89	$48.90	$48.90
Purchase #7	$91.96	8.799%	$100.0516	$100.05	$100.05	$100.10
7 purchase totals =	$751.04		$819.7541	$819.76	$819.80	$819.70