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	$171.30	4.237%	$178.558	$178.56	$178.55	$178.60
Purchase #2	$20.46	5.497%	$21.5847	$21.58	$21.60	$21.60
Purchase #3	$51.53	11.505%	$57.4585	$57.46	$57.45	$57.50
Purchase #4	$132.38	6.259%	$140.6657	$140.67	$140.65	$140.70
Purchase #5	$80.67	5.535%	$85.1351	$85.14	$85.15	$85.10
Purchase #6	$18.43	12.814%	$20.7916	$20.79	$20.80	$20.80
Purchase #7	$112.49	10.748%	$124.5804	$124.58	$124.60	$124.60
7 purchase totals =	$587.26		$628.7740	$628.78	$628.80	$628.90