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	$51.83	10.747%	$57.4002	$57.40	$57.40	$57.40
Purchase #2	$55.83	10.311%	$61.5866	$61.59	$61.60	$61.60
Purchase #3	$95.71	13.410%	$108.5447	$108.54	$108.55	$108.50
Purchase #4	$70.46	7.833%	$75.9791	$75.98	$76.00	$76.00
Purchase #5	$148.31	13.839%	$168.8346	$168.83	$168.85	$168.80
Purchase #6	$53.64	12.181%	$60.1739	$60.17	$60.15	$60.20
Purchase #7	$231.63	7.147%	$248.1846	$248.18	$248.20	$248.20
7 purchase totals =	$707.41		$780.7037	$780.69	$780.75	$780.70