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	$110.67	8.780%	$120.3868	$120.39	$120.40	$120.40
Purchase #2	$9.48	5.570%	$10.008	$10.01	$10.00	$10.00
Purchase #3	$90.28	13.818%	$102.7549	$102.75	$102.75	$102.80
Purchase #4	$108.82	13.380%	$123.3801	$123.38	$123.40	$123.40
Purchase #5	$92.27	3.706%	$95.6895	$95.69	$95.70	$95.70
Purchase #6	$178.83	4.352%	$186.6127	$186.61	$186.60	$186.60
Purchase #7	$168.30	13.247%	$190.5947	$190.59	$190.60	$190.60
7 purchase totals =	$758.65		$829.4267	$829.42	$829.45	$829.50