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	$110.94	12.496%	$124.8031	$124.80	$124.80	$124.80
Purchase #2	$203.90	8.402%	$221.0317	$221.03	$221.05	$221.00
Purchase #3	$177.73	10.354%	$196.1322	$196.13	$196.15	$196.10
Purchase #4	$203.71	4.559%	$212.9971	$213.00	$213.00	$213.00
Purchase #5	$157.42	12.318%	$176.811	$176.81	$176.80	$176.80
Purchase #6	$89.60	12.540%	$100.8358	$100.84	$100.85	$100.80
Purchase #7	$125.59	13.336%	$142.3387	$142.34	$142.35	$142.30
7 purchase totals =	$1,068.89		$1,174.9496	$1,174.95	$1,175.00	$1,174.80