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	$127.70	5.398%	$134.5932	$134.59	$134.60	$134.60
Purchase #2	$49.38	10.166%	$54.4	$54.40	$54.40	$54.40
Purchase #3	$73.65	11.392%	$82.0402	$82.04	$82.05	$82.00
Purchase #4	$131.98	11.784%	$147.5325	$147.53	$147.55	$147.50
Purchase #5	$55.84	10.182%	$61.5256	$61.53	$61.55	$61.50
Purchase #6	$89.54	3.255%	$92.4545	$92.45	$92.45	$92.50
Purchase #7	$88.72	7.314%	$95.209	$95.21	$95.20	$95.20
7 purchase totals =	$616.81		$667.7550	$667.75	$667.80	$667.70