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	$30.90	8.537%	$33.5379	$33.54	$33.55	$33.50
Purchase #2	$186.69	6.502%	$198.8286	$198.83	$198.85	$198.80
Purchase #3	$212.66	12.771%	$239.8188	$239.82	$239.80	$239.80
Purchase #4	$121.69	10.826%	$134.8642	$134.86	$134.85	$134.90
Purchase #5	$85.54	5.788%	$90.4911	$90.49	$90.50	$90.50
Purchase #6	$160.53	5.466%	$169.3046	$169.30	$169.30	$169.30
Purchase #7	$98.94	4.146%	$103.0421	$103.04	$103.05	$103.00
7 purchase totals =	$896.95		$969.8873	$969.88	$969.90	$969.80