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	$55.44	6.551%	$59.0719	$59.07	$59.05	$59.10
Purchase #2	$19.32	9.480%	$21.1515	$21.15	$21.15	$21.20
Purchase #3	$241.32	10.103%	$265.7006	$265.70	$265.70	$265.70
Purchase #4	$121.29	4.820%	$127.1362	$127.14	$127.15	$127.10
Purchase #5	$168.50	4.170%	$175.5265	$175.53	$175.55	$175.50
Purchase #6	$15.75	7.203%	$16.8845	$16.88	$16.90	$16.90
Purchase #7	$202.86	10.220%	$223.5923	$223.59	$223.60	$223.60
7 purchase totals =	$824.48		$889.0635	$889.06	$889.10	$889.10