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	$38.87	3.375%	$40.1819	$40.18	$40.20	$40.20
Purchase #2	$76.96	11.617%	$85.9004	$85.90	$85.90	$85.90
Purchase #3	$236.83	7.128%	$253.7112	$253.71	$253.70	$253.70
Purchase #4	$20.28	5.873%	$21.471	$21.47	$21.45	$21.50
Purchase #5	$46.99	9.478%	$51.4437	$51.44	$51.45	$51.40
Purchase #6	$139.57	8.541%	$151.4907	$151.49	$151.50	$151.50
Purchase #7	$20.36	7.412%	$21.8691	$21.87	$21.85	$21.90
7 purchase totals =	$579.86		$626.0680	$626.06	$626.05	$626.10