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	$121.60	10.336%	$134.1686	$134.17	$134.15	$134.20
Purchase #2	$112.97	9.217%	$123.3824	$123.38	$123.40	$123.40
Purchase #3	$153.63	6.758%	$164.0123	$164.01	$164.00	$164.00
Purchase #4	$134.59	4.818%	$141.0745	$141.07	$141.05	$141.10
Purchase #5	$193.93	12.415%	$218.0064	$218.01	$218.00	$218.00
Purchase #6	$89.28	12.560%	$100.4936	$100.49	$100.50	$100.50
Purchase #7	$89.82	10.275%	$99.049	$99.05	$99.05	$99.00
7 purchase totals =	$895.82		$980.1868	$980.18	$980.15	$980.20