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	$48.63	5.421%	$51.2662	$51.27	$51.25	$51.30
Purchase #2	$28.51	11.201%	$31.7034	$31.70	$31.70	$31.70
Purchase #3	$94.70	4.393%	$98.8602	$98.86	$98.85	$98.90
Purchase #4	$80.79	10.178%	$89.0128	$89.01	$89.00	$89.00
Purchase #5	$99.57	5.178%	$104.7257	$104.73	$104.75	$104.70
Purchase #6	$11.33	12.335%	$12.7276	$12.73	$12.75	$12.70
Purchase #7	$189.64	13.667%	$215.5581	$215.56	$215.55	$215.60
7 purchase totals =	$553.17		$603.8540	$603.86	$603.85	$603.90