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	$124.54	11.807%	$139.2444	$139.24	$139.25	$139.20
Purchase #2	$135.63	11.789%	$151.6194	$151.62	$151.60	$151.60
Purchase #3	$26.74	6.289%	$28.4217	$28.42	$28.40	$28.40
Purchase #4	$211.39	12.843%	$238.5388	$238.54	$238.55	$238.50
Purchase #5	$250.50	8.723%	$272.3511	$272.35	$272.35	$272.40
Purchase #6	$247.29	3.509%	$255.9674	$255.97	$255.95	$256.00
Purchase #7	$63.48	3.377%	$65.6237	$65.62	$65.60	$65.60
7 purchase totals =	$1,059.57		$1,151.7665	$1,151.76	$1,151.70	$1,151.70