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	$153.57	11.860%	$171.7834	$171.78	$171.80	$171.80
Purchase #2	$151.77	3.757%	$157.472	$157.47	$157.45	$157.50
Purchase #3	$146.69	3.257%	$151.4677	$151.47	$151.45	$151.50
Purchase #4	$58.55	8.525%	$63.5414	$63.54	$63.55	$63.50
Purchase #5	$172.31	3.306%	$178.0066	$178.01	$178.00	$178.00
Purchase #6	$110.55	11.855%	$123.6557	$123.66	$123.65	$123.70
Purchase #7	$139.70	5.576%	$147.4897	$147.49	$147.50	$147.50
7 purchase totals =	$933.14		$993.4165	$993.42	$993.40	$993.50