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	$76.69	7.481%	$82.4272	$82.43	$82.45	$82.40
Purchase #2	$68.49	6.275%	$72.7877	$72.79	$72.80	$72.80
Purchase #3	$16.82	7.673%	$18.1106	$18.11	$18.10	$18.10
Purchase #4	$242.71	9.795%	$266.4834	$266.48	$266.50	$266.50
Purchase #5	$50.74	3.759%	$52.6473	$52.65	$52.65	$52.60
Purchase #6	$31.97	6.198%	$33.9515	$33.95	$33.95	$34.00
Purchase #7	$82.87	8.308%	$89.7548	$89.75	$89.75	$89.80
7 purchase totals =	$570.29		$616.1625	$616.16	$616.20	$616.20