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	$41.72	3.640%	$43.2386	$43.24	$43.25	$43.20
Purchase #2	$157.60	4.590%	$164.8338	$164.83	$164.85	$164.80
Purchase #3	$35.83	8.417%	$38.8458	$38.85	$38.85	$38.80
Purchase #4	$155.32	10.414%	$171.495	$171.50	$171.50	$171.50
Purchase #5	$240.50	10.147%	$264.9035	$264.90	$264.90	$264.90
Purchase #6	$32.94	10.613%	$36.4359	$36.44	$36.45	$36.40
Purchase #7	$24.88	13.607%	$28.2654	$28.27	$28.25	$28.30
7 purchase totals =	$688.79		$748.0180	$748.03	$748.05	$747.90