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	$30.81	10.571%	$34.0669	$34.07	$34.05	$34.10
Purchase #2	$30.92	11.177%	$34.3759	$34.38	$34.40	$34.40
Purchase #3	$134.96	3.781%	$140.0628	$140.06	$140.05	$140.10
Purchase #4	$50.69	8.584%	$55.0412	$55.04	$55.05	$55.00
Purchase #5	$43.32	5.356%	$45.6402	$45.64	$45.65	$45.60
Purchase #6	$53.45	7.511%	$57.4646	$57.46	$57.45	$57.50
Purchase #7	$60.69	11.168%	$67.4679	$67.47	$67.45	$67.50
7 purchase totals =	$404.84		$434.1195	$434.12	$434.10	$434.20