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	$160.35	7.338%	$172.1165	$172.12	$172.10	$172.10
Purchase #2	$92.80	11.284%	$103.2716	$103.27	$103.25	$103.30
Purchase #3	$63.53	3.432%	$65.7103	$65.71	$65.70	$65.70
Purchase #4	$184.69	9.545%	$202.3187	$202.32	$202.30	$202.30
Purchase #5	$106.82	10.374%	$117.9015	$117.90	$117.90	$117.90
Purchase #6	$142.54	10.591%	$157.6364	$157.64	$157.65	$157.60
Purchase #7	$83.30	7.450%	$89.5059	$89.51	$89.50	$89.50
7 purchase totals =	$834.03		$908.4609	$908.47	$908.40	$908.40