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	$104.44	7.102%	$111.8573	$111.86	$111.85	$111.90
Purchase #2	$164.35	11.271%	$182.8739	$182.87	$182.85	$182.90
Purchase #3	$106.95	8.200%	$115.7199	$115.72	$115.70	$115.70
Purchase #4	$212.35	10.480%	$234.6043	$234.60	$234.60	$234.60
Purchase #5	$132.46	3.549%	$137.161	$137.16	$137.15	$137.20
Purchase #6	$117.53	8.155%	$127.1146	$127.11	$127.10	$127.10
Purchase #7	$114.72	13.596%	$130.3173	$130.32	$130.30	$130.30
7 purchase totals =	$952.80		$1,039.6483	$1,039.64	$1,039.55	$1,039.70