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	$17.59	12.738%	$19.8306	$19.83	$19.85	$19.80
Purchase #2	$137.86	11.719%	$154.0158	$154.02	$154.00	$154.00
Purchase #3	$82.82	12.869%	$93.4781	$93.48	$93.50	$93.50
Purchase #4	$78.54	5.181%	$82.6092	$82.61	$82.60	$82.60
Purchase #5	$110.54	10.157%	$121.7675	$121.77	$121.75	$121.80
Purchase #6	$248.28	6.348%	$264.0408	$264.04	$264.05	$264.00
Purchase #7	$145.65	3.551%	$150.822	$150.82	$150.80	$150.80
7 purchase totals =	$821.28		$886.5640	$886.57	$886.55	$886.50