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	$225.53	11.650%	$251.8042	$251.80	$251.80	$251.80
Purchase #2	$117.91	4.550%	$123.2749	$123.27	$123.25	$123.30
Purchase #3	$221.31	10.189%	$243.8593	$243.86	$243.85	$243.90
Purchase #4	$240.35	12.874%	$271.2927	$271.29	$271.30	$271.30
Purchase #5	$204.29	13.697%	$232.2716	$232.27	$232.25	$232.30
Purchase #6	$77.92	9.766%	$85.5297	$85.53	$85.55	$85.50
Purchase #7	$116.78	12.500%	$131.3775	$131.38	$131.40	$131.40
7 purchase totals =	$1,204.09		$1,339.4099	$1,339.40	$1,339.40	$1,339.50