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	$67.70	12.460%	$76.1354	$76.14	$76.15	$76.10
Purchase #2	$228.40	4.853%	$239.4843	$239.48	$239.50	$239.50
Purchase #3	$39.83	7.342%	$42.7543	$42.75	$42.75	$42.80
Purchase #4	$87.92	6.720%	$93.8282	$93.83	$93.85	$93.80
Purchase #5	$55.65	6.154%	$59.0747	$59.07	$59.05	$59.10
Purchase #6	$60.79	5.689%	$64.2483	$64.25	$64.25	$64.20
Purchase #7	$102.30	6.698%	$109.1521	$109.15	$109.15	$109.20
7 purchase totals =	$642.59		$684.6773	$684.67	$684.70	$684.70