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	$88.95	13.286%	$100.7679	$100.77	$100.75	$100.80
Purchase #2	$242.77	9.261%	$265.2529	$265.25	$265.25	$265.30
Purchase #3	$43.67	3.250%	$45.0893	$45.09	$45.10	$45.10
Purchase #4	$80.34	12.229%	$90.1648	$90.16	$90.15	$90.20
Purchase #5	$148.53	10.737%	$164.4777	$164.48	$164.50	$164.50
Purchase #6	$33.38	5.284%	$35.1438	$35.14	$35.15	$35.10
Purchase #7	$160.99	4.853%	$168.8028	$168.80	$168.80	$168.80
7 purchase totals =	$798.63		$869.6992	$869.69	$869.70	$869.80