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	$88.35	13.625%	$100.3877	$100.39	$100.40	$100.40
Purchase #2	$72.37	9.794%	$79.4579	$79.46	$79.45	$79.50
Purchase #3	$97.29	12.198%	$109.1574	$109.16	$109.15	$109.20
Purchase #4	$125.96	9.506%	$137.9338	$137.93	$137.95	$137.90
Purchase #5	$212.46	3.451%	$219.792	$219.79	$219.80	$219.80
Purchase #6	$41.83	11.362%	$46.5827	$46.58	$46.60	$46.60
Purchase #7	$27.60	6.302%	$29.3394	$29.34	$29.35	$29.30
7 purchase totals =	$665.86		$722.6509	$722.65	$722.70	$722.70