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	$183.33	12.639%	$206.5011	$206.50	$206.50	$206.50
Purchase #2	$136.94	9.409%	$149.8247	$149.82	$149.80	$149.80
Purchase #3	$21.28	7.477%	$22.8711	$22.87	$22.85	$22.90
Purchase #4	$35.60	4.660%	$37.259	$37.26	$37.25	$37.30
Purchase #5	$240.85	6.548%	$256.6209	$256.62	$256.60	$256.60
Purchase #6	$155.46	6.349%	$165.3302	$165.33	$165.35	$165.30
Purchase #7	$83.32	13.366%	$94.4566	$94.46	$94.45	$94.50
7 purchase totals =	$856.78		$932.8636	$932.86	$932.80	$932.90