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	$36.34	10.608%	$40.1949	$40.19	$40.20	$40.20
Purchase #2	$182.92	4.217%	$190.6337	$190.63	$190.65	$190.60
Purchase #3	$96.72	3.566%	$100.169	$100.17	$100.15	$100.20
Purchase #4	$31.81	4.195%	$33.1444	$33.14	$33.15	$33.10
Purchase #5	$116.81	7.528%	$125.6035	$125.60	$125.60	$125.60
Purchase #6	$124.57	7.299%	$133.6624	$133.66	$133.65	$133.70
Purchase #7	$191.26	12.820%	$215.7795	$215.78	$215.80	$215.80
7 purchase totals =	$780.43		$839.1874	$839.17	$839.20	$839.20