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	$19.95	7.185%	$21.3834	$21.38	$21.40	$21.40
Purchase #2	$60.83	9.263%	$66.4647	$66.46	$66.45	$66.50
Purchase #3	$115.39	13.507%	$130.9757	$130.98	$131.00	$131.00
Purchase #4	$98.73	5.177%	$103.8413	$103.84	$103.85	$103.80
Purchase #5	$112.40	5.645%	$118.745	$118.75	$118.75	$118.70
Purchase #6	$55.81	13.433%	$63.307	$63.31	$63.30	$63.30
Purchase #7	$35.95	3.563%	$37.2309	$37.23	$37.25	$37.20
7 purchase totals =	$499.06		$541.9480	$541.95	$542.00	$541.90