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	$202.87	9.577%	$222.2989	$222.30	$222.30	$222.30
Purchase #2	$171.28	6.223%	$181.9388	$181.94	$181.95	$181.90
Purchase #3	$169.57	10.652%	$187.6326	$187.63	$187.65	$187.60
Purchase #4	$63.51	3.768%	$65.9031	$65.90	$65.90	$65.90
Purchase #5	$96.26	6.630%	$102.642	$102.64	$102.65	$102.60
Purchase #6	$48.95	12.684%	$55.1588	$55.16	$55.15	$55.20
Purchase #7	$181.41	4.842%	$190.1939	$190.19	$190.20	$190.20
7 purchase totals =	$933.85		$1,005.7681	$1,005.76	$1,005.80	$1,005.70