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	$27.44	13.834%	$31.236	$31.24	$31.25	$31.20
Purchase #2	$192.94	11.374%	$214.885	$214.89	$214.90	$214.90
Purchase #3	$51.29	10.211%	$56.5272	$56.53	$56.55	$56.50
Purchase #4	$141.48	13.522%	$160.6109	$160.61	$160.60	$160.60
Purchase #5	$82.55	4.252%	$86.06	$86.06	$86.05	$86.10
Purchase #6	$165.93	4.794%	$173.8847	$173.88	$173.90	$173.90
Purchase #7	$22.62	13.558%	$25.6868	$25.69	$25.70	$25.70
7 purchase totals =	$684.25		$748.8906	$748.90	$748.95	$748.90