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	$13.87	13.497%	$15.742	$15.74	$15.75	$15.70
Purchase #2	$242.30	12.349%	$272.2216	$272.22	$272.20	$272.20
Purchase #3	$101.56	7.142%	$108.8134	$108.81	$108.80	$108.80
Purchase #4	$202.80	7.734%	$218.4846	$218.48	$218.50	$218.50
Purchase #5	$110.36	12.256%	$123.8857	$123.89	$123.90	$123.90
Purchase #6	$95.91	10.256%	$105.7465	$105.75	$105.75	$105.70
Purchase #7	$10.31	11.389%	$11.4842	$11.48	$11.50	$11.50
7 purchase totals =	$777.11		$856.3780	$856.37	$856.40	$856.30