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	$230.50	3.869%	$239.418	$239.42	$239.40	$239.40
Purchase #2	$215.47	11.870%	$241.0463	$241.05	$241.05	$241.00
Purchase #3	$68.69	4.133%	$71.529	$71.53	$71.55	$71.50
Purchase #4	$90.81	3.868%	$94.3225	$94.32	$94.30	$94.30
Purchase #5	$182.82	7.133%	$195.8606	$195.86	$195.85	$195.90
Purchase #6	$126.40	3.667%	$131.0351	$131.04	$131.05	$131.00
Purchase #7	$31.34	3.797%	$32.53	$32.53	$32.55	$32.50
7 purchase totals =	$946.03		$1,005.7415	$1,005.75	$1,005.75	$1,005.60