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	$145.74	9.186%	$159.1277	$159.13	$159.15	$159.10
Purchase #2	$90.76	7.738%	$97.783	$97.78	$97.80	$97.80
Purchase #3	$230.35	4.215%	$240.0593	$240.06	$240.05	$240.10
Purchase #4	$110.67	11.627%	$123.5376	$123.54	$123.55	$123.50
Purchase #5	$19.78	3.301%	$20.4329	$20.43	$20.45	$20.40
Purchase #6	$241.47	6.408%	$256.9434	$256.94	$256.95	$256.90
Purchase #7	$207.72	5.365%	$218.8642	$218.86	$218.85	$218.90
7 purchase totals =	$1,046.49		$1,116.7481	$1,116.74	$1,116.80	$1,116.70