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	$238.48	12.699%	$268.7646	$268.76	$268.75	$268.80
Purchase #2	$87.86	5.196%	$92.4252	$92.43	$92.45	$92.40
Purchase #3	$20.39	7.225%	$21.8632	$21.86	$21.85	$21.90
Purchase #4	$149.90	12.654%	$168.8683	$168.87	$168.85	$168.90
Purchase #5	$12.98	10.697%	$14.3685	$14.37	$14.35	$14.40
Purchase #6	$7.55	12.172%	$8.469	$8.47	$8.45	$8.50
Purchase #7	$205.41	5.158%	$216.005	$216.01	$216.00	$216.00
7 purchase totals =	$722.57		$790.7638	$790.77	$790.70	$790.90