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	$18.55	10.511%	$20.4998	$20.50	$20.50	$20.50
Purchase #2	$40.70	4.845%	$42.6719	$42.67	$42.65	$42.70
Purchase #3	$131.46	4.445%	$137.3034	$137.30	$137.30	$137.30
Purchase #4	$192.74	11.776%	$215.4371	$215.44	$215.45	$215.40
Purchase #5	$89.39	5.643%	$94.4343	$94.43	$94.45	$94.40
Purchase #6	$50.55	3.247%	$52.1914	$52.19	$52.20	$52.20
Purchase #7	$136.71	8.400%	$148.1936	$148.19	$148.20	$148.20
7 purchase totals =	$660.10		$710.7315	$710.72	$710.75	$710.70