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	$102.62	13.842%	$116.8247	$116.82	$116.80	$116.80
Purchase #2	$19.57	11.535%	$21.8274	$21.83	$21.85	$21.80
Purchase #3	$55.76	10.440%	$61.5813	$61.58	$61.60	$61.60
Purchase #4	$191.87	10.131%	$211.3083	$211.31	$211.30	$211.30
Purchase #5	$75.32	4.748%	$78.8962	$78.90	$78.90	$78.90
Purchase #6	$42.85	8.403%	$46.4507	$46.45	$46.45	$46.50
Purchase #7	$15.59	6.638%	$16.6249	$16.62	$16.60	$16.60
7 purchase totals =	$503.58		$553.5135	$553.51	$553.50	$553.50