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	$160.65	11.783%	$179.5794	$179.58	$179.60	$179.60
Purchase #2	$120.84	13.347%	$136.9685	$136.97	$136.95	$137.00
Purchase #3	$18.63	13.124%	$21.075	$21.08	$21.10	$21.10
Purchase #4	$139.98	6.831%	$149.542	$149.54	$149.55	$149.50
Purchase #5	$92.96	3.164%	$95.9013	$95.90	$95.90	$95.90
Purchase #6	$99.30	6.211%	$105.4675	$105.47	$105.45	$105.50
Purchase #7	$154.47	10.648%	$170.918	$170.92	$170.90	$170.90
7 purchase totals =	$786.83		$859.4517	$859.46	$859.45	$859.50