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	$138.30	13.811%	$157.4006	$157.40	$157.40	$157.40
Purchase #2	$85.69	3.820%	$88.9634	$88.96	$88.95	$89.00
Purchase #3	$54.73	9.298%	$59.8188	$59.82	$59.80	$59.80
Purchase #4	$191.95	12.108%	$215.1913	$215.19	$215.20	$215.20
Purchase #5	$74.64	7.870%	$80.5142	$80.51	$80.50	$80.50
Purchase #6	$61.72	8.175%	$66.7656	$66.77	$66.75	$66.80
Purchase #7	$210.27	5.476%	$221.7844	$221.78	$221.80	$221.80
7 purchase totals =	$817.30		$890.4383	$890.43	$890.40	$890.50