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	$224.53	11.402%	$250.1309	$250.13	$250.15	$250.10
Purchase #2	$80.88	12.336%	$90.8574	$90.86	$90.85	$90.90
Purchase #3	$70.66	7.490%	$75.9524	$75.95	$75.95	$76.00
Purchase #4	$6.42	6.723%	$6.8516	$6.85	$6.85	$6.90
Purchase #5	$9.62	13.514%	$10.92	$10.92	$10.90	$10.90
Purchase #6	$93.94	6.153%	$99.7201	$99.72	$99.70	$99.70
Purchase #7	$103.96	10.514%	$114.8904	$114.89	$114.90	$114.90
7 purchase totals =	$590.01		$649.3228	$649.32	$649.30	$649.40