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	$56.80	9.469%	$62.1784	$62.18	$62.20	$62.20
Purchase #2	$134.42	5.743%	$142.1397	$142.14	$142.15	$142.10
Purchase #3	$113.31	3.316%	$117.0674	$117.07	$117.05	$117.10
Purchase #4	$42.34	3.654%	$43.8871	$43.89	$43.90	$43.90
Purchase #5	$123.56	11.194%	$137.3913	$137.39	$137.40	$137.40
Purchase #6	$120.88	5.297%	$127.283	$127.28	$127.30	$127.30
Purchase #7	$10.55	7.699%	$11.3622	$11.36	$11.35	$11.40
7 purchase totals =	$601.86		$641.3091	$641.31	$641.35	$641.40