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	$31.97	7.779%	$34.4569	$34.46	$34.45	$34.50
Purchase #2	$20.33	7.680%	$21.8913	$21.89	$21.90	$21.90
Purchase #3	$19.25	4.803%	$20.1746	$20.17	$20.15	$20.20
Purchase #4	$150.71	7.236%	$161.6154	$161.62	$161.60	$161.60
Purchase #5	$37.93	5.227%	$39.9126	$39.91	$39.90	$39.90
Purchase #6	$35.54	12.618%	$40.0244	$40.02	$40.00	$40.00
Purchase #7	$174.28	9.726%	$191.2305	$191.23	$191.25	$191.20
7 purchase totals =	$470.01		$509.3057	$509.30	$509.25	$509.30