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	$249.76	12.401%	$280.7327	$280.73	$280.75	$280.70
Purchase #2	$233.27	8.744%	$253.6671	$253.67	$253.65	$253.70
Purchase #3	$115.30	13.161%	$130.4746	$130.47	$130.45	$130.50
Purchase #4	$168.26	13.825%	$191.5219	$191.52	$191.50	$191.50
Purchase #5	$65.77	10.123%	$72.4279	$72.43	$72.45	$72.40
Purchase #6	$128.43	7.646%	$138.2498	$138.25	$138.25	$138.20
Purchase #7	$202.90	11.628%	$226.4932	$226.49	$226.50	$226.50
7 purchase totals =	$1,163.69		$1,293.5672	$1,293.56	$1,293.55	$1,293.50