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	$190.42	6.492%	$202.7821	$202.78	$202.80	$202.80
Purchase #2	$139.56	8.617%	$151.5859	$151.59	$151.60	$151.60
Purchase #3	$61.71	5.102%	$64.8584	$64.86	$64.85	$64.90
Purchase #4	$58.87	3.841%	$61.1312	$61.13	$61.15	$61.10
Purchase #5	$40.72	3.810%	$42.2714	$42.27	$42.25	$42.30
Purchase #6	$138.54	9.533%	$151.747	$151.75	$151.75	$151.70
Purchase #7	$197.98	13.557%	$224.8201	$224.82	$224.80	$224.80
7 purchase totals =	$827.80		$899.1961	$899.20	$899.20	$899.20