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	$119.48	6.340%	$127.055	$127.06	$127.05	$127.10
Purchase #2	$127.92	9.312%	$139.8319	$139.83	$139.85	$139.80
Purchase #3	$84.90	7.381%	$91.1665	$91.17	$91.15	$91.20
Purchase #4	$51.58	9.560%	$56.511	$56.51	$56.50	$56.50
Purchase #5	$100.34	8.422%	$108.7906	$108.79	$108.80	$108.80
Purchase #6	$224.53	9.523%	$245.912	$245.91	$245.90	$245.90
Purchase #7	$132.57	13.776%	$150.8328	$150.83	$150.85	$150.80
7 purchase totals =	$841.32		$920.0998	$920.10	$920.10	$920.10