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	$42.75	6.451%	$45.5078	$45.51	$45.50	$45.50
Purchase #2	$212.97	6.805%	$227.4626	$227.46	$227.45	$227.50
Purchase #3	$201.29	9.258%	$219.9254	$219.93	$219.95	$219.90
Purchase #4	$159.98	3.840%	$166.1232	$166.12	$166.10	$166.10
Purchase #5	$78.45	4.800%	$82.2156	$82.22	$82.20	$82.20
Purchase #6	$123.85	11.784%	$138.4445	$138.44	$138.45	$138.40
Purchase #7	$239.35	10.789%	$265.1735	$265.17	$265.15	$265.20
7 purchase totals =	$1,058.64		$1,144.8526	$1,144.85	$1,144.80	$1,144.80