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	$18.39	7.617%	$19.7908	$19.79	$19.80	$19.80
Purchase #2	$89.55	12.746%	$100.964	$100.96	$100.95	$101.00
Purchase #3	$152.38	12.128%	$170.8606	$170.86	$170.85	$170.90
Purchase #4	$85.92	9.792%	$94.3333	$94.33	$94.35	$94.30
Purchase #5	$203.45	9.628%	$223.0382	$223.04	$223.05	$223.00
Purchase #6	$81.37	11.118%	$90.4167	$90.42	$90.40	$90.40
Purchase #7	$101.72	3.598%	$105.3799	$105.38	$105.40	$105.40
7 purchase totals =	$732.78		$804.7835	$804.78	$804.80	$804.80