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	$126.36	6.685%	$134.8072	$134.81	$134.80	$134.80
Purchase #2	$188.93	3.573%	$195.6805	$195.68	$195.70	$195.70
Purchase #3	$95.43	4.666%	$99.8828	$99.88	$99.90	$99.90
Purchase #4	$127.89	10.716%	$141.5947	$141.59	$141.60	$141.60
Purchase #5	$202.46	3.856%	$210.2669	$210.27	$210.25	$210.30
Purchase #6	$40.77	4.423%	$42.5733	$42.57	$42.55	$42.60
Purchase #7	$23.52	7.715%	$25.3346	$25.33	$25.35	$25.30
7 purchase totals =	$805.36		$850.1400	$850.13	$850.15	$850.20