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	$85.73	7.867%	$92.4744	$92.47	$92.45	$92.50
Purchase #2	$91.51	10.209%	$100.8523	$100.85	$100.85	$100.90
Purchase #3	$172.88	12.230%	$194.0232	$194.02	$194.00	$194.00
Purchase #4	$22.93	4.193%	$23.8915	$23.89	$23.90	$23.90
Purchase #5	$159.33	12.405%	$179.0949	$179.09	$179.10	$179.10
Purchase #6	$80.92	10.330%	$89.279	$89.28	$89.30	$89.30
Purchase #7	$179.40	6.334%	$190.7632	$190.76	$190.75	$190.80
7 purchase totals =	$792.70		$870.3785	$870.36	$870.35	$870.50