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	$10.28	12.172%	$11.5313	$11.53	$11.55	$11.50
Purchase #2	$111.95	4.860%	$117.3908	$117.39	$117.40	$117.40
Purchase #3	$80.62	6.625%	$85.9611	$85.96	$85.95	$86.00
Purchase #4	$229.64	7.795%	$247.5404	$247.54	$247.55	$247.50
Purchase #5	$121.98	8.660%	$132.5435	$132.54	$132.55	$132.50
Purchase #6	$223.78	6.504%	$238.3347	$238.33	$238.35	$238.30
Purchase #7	$11.63	13.274%	$13.1738	$13.17	$13.15	$13.20
7 purchase totals =	$789.88		$846.4756	$846.46	$846.50	$846.40