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	$16.59	8.716%	$18.036	$18.04	$18.05	$18.00
Purchase #2	$27.67	11.789%	$30.932	$30.93	$30.95	$30.90
Purchase #3	$249.66	4.739%	$261.4914	$261.49	$261.50	$261.50
Purchase #4	$73.75	6.415%	$78.4811	$78.48	$78.50	$78.50
Purchase #5	$33.83	10.608%	$37.4187	$37.42	$37.40	$37.40
Purchase #6	$116.73	13.513%	$132.5037	$132.50	$132.50	$132.50
Purchase #7	$82.95	3.626%	$85.9578	$85.96	$85.95	$86.00
7 purchase totals =	$601.18		$644.8207	$644.82	$644.85	$644.80