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	$131.42	4.573%	$137.4298	$137.43	$137.45	$137.40
Purchase #2	$224.62	6.315%	$238.8048	$238.80	$238.80	$238.80
Purchase #3	$158.75	3.664%	$164.5666	$164.57	$164.55	$164.60
Purchase #4	$53.67	11.499%	$59.8415	$59.84	$59.85	$59.80
Purchase #5	$26.93	13.595%	$30.5911	$30.59	$30.60	$30.60
Purchase #6	$127.67	10.709%	$141.3422	$141.34	$141.35	$141.30
Purchase #7	$129.65	3.227%	$133.8338	$133.83	$133.85	$133.80
7 purchase totals =	$852.71		$906.4098	$906.40	$906.45	$906.30