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	$225.52	13.516%	$256.0013	$256.00	$256.00	$256.00
Purchase #2	$84.84	6.105%	$90.0195	$90.02	$90.00	$90.00
Purchase #3	$166.36	9.648%	$182.4104	$182.41	$182.40	$182.40
Purchase #4	$121.27	5.307%	$127.7058	$127.71	$127.70	$127.70
Purchase #5	$30.28	6.334%	$32.1979	$32.20	$32.20	$32.20
Purchase #6	$45.88	5.123%	$48.2304	$48.23	$48.25	$48.20
Purchase #7	$78.47	5.812%	$83.0307	$83.03	$83.05	$83.00
7 purchase totals =	$752.62		$819.5960	$819.60	$819.60	$819.50