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	$127.25	9.116%	$138.8501	$138.85	$138.85	$138.90
Purchase #2	$35.89	6.661%	$38.2806	$38.28	$38.30	$38.30
Purchase #3	$233.85	13.145%	$264.5896	$264.59	$264.60	$264.60
Purchase #4	$39.85	6.477%	$42.4311	$42.43	$42.45	$42.40
Purchase #5	$8.88	10.466%	$9.8094	$9.81	$9.80	$9.80
Purchase #6	$152.77	6.532%	$162.7489	$162.75	$162.75	$162.70
Purchase #7	$186.86	13.760%	$212.5719	$212.57	$212.55	$212.60
7 purchase totals =	$785.35		$869.2816	$869.28	$869.30	$869.30