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	$244.82	4.232%	$255.1808	$255.18	$255.20	$255.20
Purchase #2	$158.39	6.191%	$168.1959	$168.20	$168.20	$168.20
Purchase #3	$59.53	6.163%	$63.1988	$63.20	$63.20	$63.20
Purchase #4	$33.58	8.200%	$36.3336	$36.33	$36.35	$36.30
Purchase #5	$164.60	8.175%	$178.0561	$178.06	$178.05	$178.10
Purchase #6	$209.84	13.549%	$238.2712	$238.27	$238.25	$238.30
Purchase #7	$89.73	11.645%	$100.1791	$100.18	$100.20	$100.20
7 purchase totals =	$960.49		$1,039.4155	$1,039.42	$1,039.45	$1,039.50