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	$206.88	4.169%	$215.5048	$215.50	$215.50	$215.50
Purchase #2	$64.48	3.181%	$66.5311	$66.53	$66.55	$66.50
Purchase #3	$212.79	6.129%	$225.8319	$225.83	$225.85	$225.80
Purchase #4	$37.87	12.502%	$42.6045	$42.60	$42.60	$42.60
Purchase #5	$122.82	12.298%	$137.9244	$137.92	$137.90	$137.90
Purchase #6	$5.83	7.494%	$6.2669	$6.27	$6.25	$6.30
Purchase #7	$176.65	10.336%	$194.9085	$194.91	$194.90	$194.90
7 purchase totals =	$827.32		$889.5721	$889.56	$889.55	$889.50