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	$121.78	8.297%	$131.8841	$131.88	$131.90	$131.90
Purchase #2	$141.45	12.718%	$159.4396	$159.44	$159.45	$159.40
Purchase #3	$35.45	11.655%	$39.5817	$39.58	$39.60	$39.60
Purchase #4	$198.54	8.693%	$215.7991	$215.80	$215.80	$215.80
Purchase #5	$27.27	9.185%	$29.7747	$29.77	$29.75	$29.80
Purchase #6	$137.96	10.249%	$152.0995	$152.10	$152.10	$152.10
Purchase #7	$119.85	11.836%	$134.0354	$134.04	$134.05	$134.00
7 purchase totals =	$782.30		$862.6141	$862.61	$862.65	$862.60