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	$240.68	6.703%	$256.8128	$256.81	$256.80	$256.80
Purchase #2	$21.40	4.738%	$22.4139	$22.41	$22.40	$22.40
Purchase #3	$31.48	6.290%	$33.4601	$33.46	$33.45	$33.50
Purchase #4	$177.40	4.772%	$185.8655	$185.87	$185.85	$185.90
Purchase #5	$112.86	9.870%	$123.9993	$124.00	$124.00	$124.00
Purchase #6	$54.83	5.785%	$58.0019	$58.00	$58.00	$58.00
Purchase #7	$161.47	4.569%	$168.8476	$168.85	$168.85	$168.80
7 purchase totals =	$800.12		$849.4011	$849.40	$849.35	$849.40