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	$248.58	4.329%	$259.341	$259.34	$259.35	$259.30
Purchase #2	$150.97	10.247%	$166.4399	$166.44	$166.45	$166.40
Purchase #3	$140.48	10.592%	$155.3596	$155.36	$155.35	$155.40
Purchase #4	$98.64	5.320%	$103.8876	$103.89	$103.90	$103.90
Purchase #5	$195.51	7.529%	$210.2299	$210.23	$210.25	$210.20
Purchase #6	$87.59	12.857%	$98.8514	$98.85	$98.85	$98.90
Purchase #7	$145.75	13.503%	$165.4306	$165.43	$165.45	$165.40
7 purchase totals =	$1,067.52		$1,159.5400	$1,159.54	$1,159.60	$1,159.50