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	$36.70	7.704%	$39.5274	$39.53	$39.55	$39.50
Purchase #2	$218.74	13.863%	$249.0639	$249.06	$249.05	$249.10
Purchase #3	$38.31	12.740%	$43.1907	$43.19	$43.20	$43.20
Purchase #4	$169.50	12.552%	$190.7756	$190.78	$190.80	$190.80
Purchase #5	$99.70	8.328%	$108.003	$108.00	$108.00	$108.00
Purchase #6	$243.82	10.845%	$270.2623	$270.26	$270.25	$270.30
Purchase #7	$243.66	4.858%	$255.497	$255.50	$255.50	$255.50
7 purchase totals =	$1,050.43		$1,156.3199	$1,156.32	$1,156.35	$1,156.40