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	$25.97	5.210%	$27.323	$27.32	$27.30	$27.30
Purchase #2	$159.89	5.688%	$168.9845	$168.98	$169.00	$169.00
Purchase #3	$232.72	9.342%	$254.4607	$254.46	$254.45	$254.50
Purchase #4	$165.85	12.109%	$185.9328	$185.93	$185.95	$185.90
Purchase #5	$64.39	6.510%	$68.5818	$68.58	$68.60	$68.60
Purchase #6	$145.35	8.432%	$157.6059	$157.61	$157.60	$157.60
Purchase #7	$218.47	8.544%	$237.1361	$237.14	$237.15	$237.10
7 purchase totals =	$1,012.64		$1,100.0248	$1,100.02	$1,100.05	$1,100.00