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	$90.37	10.704%	$100.0432	$100.04	$100.05	$100.00
Purchase #2	$199.49	5.424%	$210.3103	$210.31	$210.30	$210.30
Purchase #3	$190.85	9.309%	$208.6162	$208.62	$208.60	$208.60
Purchase #4	$171.32	7.226%	$183.6996	$183.70	$183.70	$183.70
Purchase #5	$61.71	10.554%	$68.2229	$68.22	$68.20	$68.20
Purchase #6	$98.39	5.197%	$103.5033	$103.50	$103.50	$103.50
Purchase #7	$104.59	4.568%	$109.3677	$109.37	$109.35	$109.40
7 purchase totals =	$916.72		$983.7632	$983.76	$983.70	$983.70