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	$171.72	3.842%	$178.3175	$178.32	$178.30	$178.30
Purchase #2	$234.75	5.587%	$247.8655	$247.87	$247.85	$247.90
Purchase #3	$97.98	11.854%	$109.5945	$109.59	$109.60	$109.60
Purchase #4	$249.55	12.230%	$280.07	$280.07	$280.05	$280.10
Purchase #5	$69.46	13.370%	$78.7468	$78.75	$78.75	$78.70
Purchase #6	$167.50	6.561%	$178.4897	$178.49	$178.50	$178.50
Purchase #7	$63.98	7.327%	$68.6678	$68.67	$68.65	$68.70
7 purchase totals =	$1,054.94		$1,141.7518	$1,141.76	$1,141.70	$1,141.80