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	$40.25	8.789%	$43.7876	$43.79	$43.80	$43.80
Purchase #2	$53.73	10.608%	$59.4297	$59.43	$59.45	$59.40
Purchase #3	$67.96	8.680%	$73.8589	$73.86	$73.85	$73.90
Purchase #4	$149.90	11.590%	$167.2734	$167.27	$167.25	$167.30
Purchase #5	$69.48	11.672%	$77.5897	$77.59	$77.60	$77.60
Purchase #6	$93.71	11.180%	$104.1868	$104.19	$104.20	$104.20
Purchase #7	$11.74	8.624%	$12.7525	$12.75	$12.75	$12.80
7 purchase totals =	$486.77		$538.8786	$538.88	$538.90	$539.00