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	$113.84	8.405%	$123.4083	$123.41	$123.40	$123.40
Purchase #2	$93.60	6.137%	$99.3442	$99.34	$99.35	$99.30
Purchase #3	$47.60	8.126%	$51.468	$51.47	$51.45	$51.50
Purchase #4	$135.73	7.349%	$145.7048	$145.70	$145.70	$145.70
Purchase #5	$116.86	5.643%	$123.4544	$123.45	$123.45	$123.50
Purchase #6	$7.93	9.779%	$8.7055	$8.71	$8.70	$8.70
Purchase #7	$225.82	13.333%	$255.9286	$255.93	$255.95	$255.90
7 purchase totals =	$741.38		$808.0138	$808.01	$808.00	$808.00