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	$19.26	5.775%	$20.3723	$20.37	$20.35	$20.40
Purchase #2	$64.33	3.674%	$66.6935	$66.69	$66.70	$66.70
Purchase #3	$51.61	4.262%	$53.8096	$53.81	$53.80	$53.80
Purchase #4	$80.92	5.340%	$85.2411	$85.24	$85.25	$85.20
Purchase #5	$97.59	3.184%	$100.6973	$100.70	$100.70	$100.70
Purchase #6	$69.69	5.744%	$73.693	$73.69	$73.70	$73.70
Purchase #7	$127.25	11.671%	$142.1013	$142.10	$142.10	$142.10
7 purchase totals =	$510.65		$542.6081	$542.60	$542.60	$542.60