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	$248.42	9.178%	$271.22	$271.22	$271.20	$271.20
Purchase #2	$63.31	12.807%	$71.4181	$71.42	$71.40	$71.40
Purchase #3	$12.61	13.544%	$14.3179	$14.32	$14.30	$14.30
Purchase #4	$18.86	13.189%	$21.3474	$21.35	$21.35	$21.30
Purchase #5	$40.64	7.197%	$43.5649	$43.56	$43.55	$43.60
Purchase #6	$135.43	11.635%	$151.1873	$151.19	$151.20	$151.20
Purchase #7	$64.56	13.628%	$73.3582	$73.36	$73.35	$73.40
7 purchase totals =	$583.83		$646.4138	$646.42	$646.35	$646.40