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	$105.96	12.125%	$118.8077	$118.81	$118.80	$118.80
Purchase #2	$211.27	6.726%	$225.48	$225.48	$225.50	$225.50
Purchase #3	$91.42	5.378%	$96.3366	$96.34	$96.35	$96.30
Purchase #4	$230.35	8.300%	$249.4691	$249.47	$249.45	$249.50
Purchase #5	$238.94	10.401%	$263.7921	$263.79	$263.80	$263.80
Purchase #6	$20.33	3.784%	$21.0993	$21.10	$21.10	$21.10
Purchase #7	$98.37	5.159%	$103.4449	$103.44	$103.45	$103.40
7 purchase totals =	$996.64		$1,078.4297	$1,078.43	$1,078.45	$1,078.40