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	$120.85	13.147%	$136.7381	$136.74	$136.75	$136.70
Purchase #2	$71.90	7.141%	$77.0344	$77.03	$77.05	$77.00
Purchase #3	$69.76	3.819%	$72.4241	$72.42	$72.40	$72.40
Purchase #4	$113.65	3.289%	$117.3879	$117.39	$117.40	$117.40
Purchase #5	$142.39	4.605%	$148.9471	$148.95	$148.95	$148.90
Purchase #6	$70.87	13.482%	$80.4247	$80.42	$80.40	$80.40
Purchase #7	$29.67	11.698%	$33.1408	$33.14	$33.15	$33.10
7 purchase totals =	$619.09		$666.0971	$666.09	$666.10	$665.90