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	$48.84	4.252%	$50.9167	$50.92	$50.90	$50.90
Purchase #2	$200.43	12.687%	$225.8586	$225.86	$225.85	$225.90
Purchase #3	$51.86	5.801%	$54.8684	$54.87	$54.85	$54.90
Purchase #4	$125.69	4.464%	$131.3008	$131.30	$131.30	$131.30
Purchase #5	$237.36	8.242%	$256.9232	$256.92	$256.90	$256.90
Purchase #6	$148.86	7.744%	$160.3877	$160.39	$160.40	$160.40
Purchase #7	$86.69	11.461%	$96.6255	$96.63	$96.65	$96.60
7 purchase totals =	$899.73		$976.8809	$976.89	$976.85	$976.90