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	$49.81	12.812%	$56.1917	$56.19	$56.20	$56.20
Purchase #2	$200.98	7.236%	$215.5229	$215.52	$215.50	$215.50
Purchase #3	$78.93	13.803%	$89.8247	$89.82	$89.80	$89.80
Purchase #4	$57.36	13.319%	$64.9998	$65.00	$65.00	$65.00
Purchase #5	$19.62	11.227%	$21.8227	$21.82	$21.80	$21.80
Purchase #6	$13.67	13.540%	$15.5209	$15.52	$15.50	$15.50
Purchase #7	$132.27	13.535%	$150.1727	$150.17	$150.15	$150.20
7 purchase totals =	$552.64		$614.0554	$614.04	$613.95	$614.00