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	$42.40	7.814%	$45.7131	$45.71	$45.70	$45.70
Purchase #2	$193.38	10.376%	$213.4451	$213.45	$213.45	$213.40
Purchase #3	$38.46	3.827%	$39.9319	$39.93	$39.95	$39.90
Purchase #4	$164.31	5.172%	$172.8081	$172.81	$172.80	$172.80
Purchase #5	$149.83	7.700%	$161.3669	$161.37	$161.35	$161.40
Purchase #6	$119.59	10.866%	$132.5846	$132.58	$132.60	$132.60
Purchase #7	$24.35	12.835%	$27.4753	$27.48	$27.50	$27.50
7 purchase totals =	$732.32		$793.3250	$793.33	$793.35	$793.30