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	$138.89	13.508%	$157.6513	$157.65	$157.65	$157.70
Purchase #2	$77.96	7.149%	$83.5334	$83.53	$83.55	$83.50
Purchase #3	$240.82	3.528%	$249.3161	$249.32	$249.30	$249.30
Purchase #4	$52.64	12.741%	$59.3469	$59.35	$59.35	$59.30
Purchase #5	$194.42	11.697%	$217.1613	$217.16	$217.15	$217.20
Purchase #6	$84.57	5.731%	$89.4167	$89.42	$89.40	$89.40
Purchase #7	$71.68	12.683%	$80.7712	$80.77	$80.75	$80.80
7 purchase totals =	$860.98		$937.1969	$937.20	$937.15	$937.20