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	$98.38	13.180%	$111.3465	$111.35	$111.35	$111.30
Purchase #2	$107.74	6.211%	$114.4317	$114.43	$114.45	$114.40
Purchase #3	$92.36	8.520%	$100.2291	$100.23	$100.25	$100.20
Purchase #4	$75.35	9.397%	$82.4306	$82.43	$82.45	$82.40
Purchase #5	$108.44	7.281%	$116.3355	$116.34	$116.35	$116.30
Purchase #6	$80.51	3.142%	$83.0396	$83.04	$83.05	$83.00
Purchase #7	$201.46	4.246%	$210.014	$210.01	$210.00	$210.00
7 purchase totals =	$764.24		$817.8270	$817.83	$817.90	$817.60