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	$46.58	9.766%	$51.129	$51.13	$51.15	$51.10
Purchase #2	$219.41	5.708%	$231.9339	$231.93	$231.95	$231.90
Purchase #3	$187.31	13.871%	$213.2918	$213.29	$213.30	$213.30
Purchase #4	$60.42	7.789%	$65.1261	$65.13	$65.15	$65.10
Purchase #5	$18.46	4.741%	$19.3352	$19.34	$19.35	$19.30
Purchase #6	$91.51	3.138%	$94.3816	$94.38	$94.40	$94.40
Purchase #7	$178.89	9.800%	$196.4212	$196.42	$196.40	$196.40
7 purchase totals =	$802.58		$871.6188	$871.62	$871.70	$871.50