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	$170.96	3.462%	$176.8786	$176.88	$176.90	$176.90
Purchase #2	$40.78	3.373%	$42.1555	$42.16	$42.15	$42.20
Purchase #3	$18.31	11.708%	$20.4537	$20.45	$20.45	$20.50
Purchase #4	$91.39	10.183%	$100.6962	$100.70	$100.70	$100.70
Purchase #5	$79.51	9.243%	$86.8591	$86.86	$86.85	$86.90
Purchase #6	$152.85	12.524%	$171.9929	$171.99	$172.00	$172.00
Purchase #7	$55.84	4.757%	$58.4963	$58.50	$58.50	$58.50
7 purchase totals =	$609.64		$657.5323	$657.54	$657.55	$657.70