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	$109.31	13.311%	$123.8603	$123.86	$123.85	$123.90
Purchase #2	$129.47	5.383%	$136.4394	$136.44	$136.45	$136.40
Purchase #3	$147.37	8.646%	$160.1116	$160.11	$160.10	$160.10
Purchase #4	$228.30	3.301%	$235.8362	$235.84	$235.85	$235.80
Purchase #5	$44.59	9.454%	$48.8055	$48.81	$48.80	$48.80
Purchase #6	$25.40	12.585%	$28.5966	$28.60	$28.60	$28.60
Purchase #7	$54.72	13.118%	$61.8982	$61.90	$61.90	$61.90
7 purchase totals =	$739.16		$795.5478	$795.56	$795.55	$795.50