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	$32.77	12.587%	$36.8948	$36.89	$36.90	$36.90
Purchase #2	$181.51	5.170%	$190.8941	$190.89	$190.90	$190.90
Purchase #3	$27.27	13.842%	$31.0447	$31.04	$31.05	$31.00
Purchase #4	$142.45	5.737%	$150.6224	$150.62	$150.60	$150.60
Purchase #5	$224.64	9.854%	$246.776	$246.78	$246.80	$246.80
Purchase #6	$189.32	6.748%	$202.0953	$202.10	$202.10	$202.10
Purchase #7	$146.35	3.232%	$151.08	$151.08	$151.10	$151.10
7 purchase totals =	$944.31		$1,009.4073	$1,009.40	$1,009.45	$1,009.40