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	$104.86	12.331%	$117.7903	$117.79	$117.80	$117.80
Purchase #2	$42.65	13.348%	$48.3429	$48.34	$48.35	$48.30
Purchase #3	$190.75	12.846%	$215.2537	$215.25	$215.25	$215.30
Purchase #4	$109.42	3.515%	$113.2661	$113.27	$113.25	$113.30
Purchase #5	$30.32	3.824%	$31.4794	$31.48	$31.50	$31.50
Purchase #6	$231.51	13.426%	$262.5925	$262.59	$262.60	$262.60
Purchase #7	$174.30	7.543%	$187.4474	$187.45	$187.45	$187.40
7 purchase totals =	$883.81		$976.1723	$976.17	$976.20	$976.20