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	$125.48	11.470%	$139.8726	$139.87	$139.85	$139.90
Purchase #2	$29.69	10.858%	$32.9137	$32.91	$32.90	$32.90
Purchase #3	$57.91	12.754%	$65.2958	$65.30	$65.30	$65.30
Purchase #4	$73.75	3.729%	$76.5001	$76.50	$76.50	$76.50
Purchase #5	$154.31	6.825%	$164.8417	$164.84	$164.85	$164.80
Purchase #6	$71.41	13.508%	$81.0561	$81.06	$81.05	$81.10
Purchase #7	$42.80	9.329%	$46.7928	$46.79	$46.80	$46.80
7 purchase totals =	$555.35		$607.2728	$607.27	$607.25	$607.30