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	$57.37	3.480%	$59.3665	$59.37	$59.35	$59.40
Purchase #2	$151.51	6.205%	$160.9112	$160.91	$160.90	$160.90
Purchase #3	$62.54	7.314%	$67.1142	$67.11	$67.10	$67.10
Purchase #4	$76.28	10.104%	$83.9873	$83.99	$84.00	$84.00
Purchase #5	$223.44	5.823%	$236.4509	$236.45	$236.45	$236.50
Purchase #6	$60.67	5.595%	$64.0645	$64.06	$64.05	$64.10
Purchase #7	$115.51	10.165%	$127.2516	$127.25	$127.25	$127.30
7 purchase totals =	$747.32		$799.1462	$799.14	$799.10	$799.30