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	$85.39	4.104%	$88.8944	$88.89	$88.90	$88.90
Purchase #2	$127.90	10.644%	$141.5137	$141.51	$141.50	$141.50
Purchase #3	$34.84	3.676%	$36.1207	$36.12	$36.10	$36.10
Purchase #4	$203.88	6.598%	$217.332	$217.33	$217.35	$217.30
Purchase #5	$15.76	8.411%	$17.0856	$17.09	$17.10	$17.10
Purchase #6	$111.26	4.706%	$116.4959	$116.50	$116.50	$116.50
Purchase #7	$80.34	11.341%	$89.4514	$89.45	$89.45	$89.50
7 purchase totals =	$659.37		$706.8937	$706.89	$706.90	$706.90