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	$186.74	10.765%	$206.8426	$206.84	$206.85	$206.80
Purchase #2	$98.32	13.794%	$111.8823	$111.88	$111.90	$111.90
Purchase #3	$73.85	4.243%	$76.9835	$76.98	$77.00	$77.00
Purchase #4	$22.80	10.808%	$25.2642	$25.26	$25.25	$25.30
Purchase #5	$142.43	13.736%	$161.9942	$161.99	$162.00	$162.00
Purchase #6	$49.97	4.602%	$52.2696	$52.27	$52.25	$52.30
Purchase #7	$28.66	13.309%	$32.4744	$32.47	$32.45	$32.50
7 purchase totals =	$602.77		$667.7108	$667.69	$667.70	$667.80