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	$41.90	3.722%	$43.4595	$43.46	$43.45	$43.50
Purchase #2	$107.66	11.418%	$119.9526	$119.95	$119.95	$120.00
Purchase #3	$115.86	3.243%	$119.6173	$119.62	$119.60	$119.60
Purchase #4	$148.59	9.429%	$162.6006	$162.60	$162.60	$162.60
Purchase #5	$29.41	13.140%	$33.2745	$33.27	$33.25	$33.30
Purchase #6	$171.76	11.418%	$191.3716	$191.37	$191.35	$191.40
Purchase #7	$96.66	8.320%	$104.7021	$104.70	$104.70	$104.70
7 purchase totals =	$711.84		$774.9782	$774.97	$774.90	$775.10