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	$19.25	8.664%	$20.9178	$20.92	$20.90	$20.90
Purchase #2	$188.28	11.797%	$210.4914	$210.49	$210.50	$210.50
Purchase #3	$205.50	8.334%	$222.6264	$222.63	$222.65	$222.60
Purchase #4	$190.32	11.249%	$211.7291	$211.73	$211.75	$211.70
Purchase #5	$165.55	6.551%	$176.3952	$176.40	$176.40	$176.40
Purchase #6	$80.52	6.776%	$85.976	$85.98	$86.00	$86.00
Purchase #7	$53.85	3.308%	$55.6314	$55.63	$55.65	$55.60
7 purchase totals =	$903.27		$983.7673	$983.78	$983.85	$983.70