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	$178.61	4.467%	$186.5885	$186.59	$186.60	$186.60
Purchase #2	$179.53	5.727%	$189.8117	$189.81	$189.80	$189.80
Purchase #3	$34.79	10.344%	$38.3887	$38.39	$38.40	$38.40
Purchase #4	$213.87	6.431%	$227.624	$227.62	$227.60	$227.60
Purchase #5	$25.70	11.624%	$28.6874	$28.69	$28.70	$28.70
Purchase #6	$77.49	11.574%	$86.4587	$86.46	$86.45	$86.50
Purchase #7	$81.54	11.120%	$90.6072	$90.61	$90.60	$90.60
7 purchase totals =	$791.53		$848.1662	$848.17	$848.15	$848.20