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	$159.82	5.791%	$169.0752	$169.08	$169.10	$169.10
Purchase #2	$250.78	7.849%	$270.4637	$270.46	$270.45	$270.50
Purchase #3	$79.25	12.662%	$89.2846	$89.28	$89.30	$89.30
Purchase #4	$89.73	4.291%	$93.5803	$93.58	$93.60	$93.60
Purchase #5	$107.60	11.852%	$120.3528	$120.35	$120.35	$120.40
Purchase #6	$213.98	10.687%	$236.848	$236.85	$236.85	$236.80
Purchase #7	$227.62	6.503%	$242.4221	$242.42	$242.40	$242.40
7 purchase totals =	$1,128.78		$1,222.0267	$1,222.02	$1,222.05	$1,222.10