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	$200.80	7.106%	$215.0688	$215.07	$215.05	$215.10
Purchase #2	$159.56	4.406%	$166.5902	$166.59	$166.60	$166.60
Purchase #3	$111.72	6.329%	$118.7908	$118.79	$118.80	$118.80
Purchase #4	$180.25	10.659%	$199.4628	$199.46	$199.45	$199.50
Purchase #5	$18.54	12.369%	$20.8332	$20.83	$20.85	$20.80
Purchase #6	$55.54	7.199%	$59.5383	$59.54	$59.55	$59.50
Purchase #7	$54.83	10.517%	$60.5965	$60.60	$60.60	$60.60
7 purchase totals =	$781.24		$840.8806	$840.88	$840.90	$840.90