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	$81.27	11.786%	$90.8485	$90.85	$90.85	$90.80
Purchase #2	$52.44	5.377%	$55.2597	$55.26	$55.25	$55.30
Purchase #3	$245.27	4.601%	$256.5549	$256.55	$256.55	$256.60
Purchase #4	$31.28	5.729%	$33.072	$33.07	$33.05	$33.10
Purchase #5	$123.92	9.773%	$136.0307	$136.03	$136.05	$136.00
Purchase #6	$135.59	10.381%	$149.6656	$149.67	$149.65	$149.70
Purchase #7	$150.63	12.178%	$168.9737	$168.97	$168.95	$169.00
7 purchase totals =	$820.40		$890.4051	$890.40	$890.35	$890.50