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	$78.57	3.164%	$81.056	$81.06	$81.05	$81.10
Purchase #2	$18.77	6.699%	$20.0274	$20.03	$20.05	$20.00
Purchase #3	$12.90	12.656%	$14.5326	$14.53	$14.55	$14.50
Purchase #4	$123.33	7.596%	$132.6981	$132.70	$132.70	$132.70
Purchase #5	$161.60	6.768%	$172.5371	$172.54	$172.55	$172.50
Purchase #6	$120.96	12.540%	$136.1284	$136.13	$136.15	$136.10
Purchase #7	$116.82	5.483%	$123.2252	$123.23	$123.25	$123.20
7 purchase totals =	$632.95		$680.2048	$680.22	$680.30	$680.10