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	$21.72	8.815%	$23.6346	$23.63	$23.65	$23.60
Purchase #2	$112.40	6.795%	$120.0376	$120.04	$120.05	$120.00
Purchase #3	$80.61	11.521%	$89.8971	$89.90	$89.90	$89.90
Purchase #4	$95.87	10.134%	$105.5855	$105.59	$105.60	$105.60
Purchase #5	$88.57	3.753%	$91.894	$91.89	$91.90	$91.90
Purchase #6	$236.50	10.328%	$260.9257	$260.93	$260.95	$260.90
Purchase #7	$114.35	3.487%	$118.3374	$118.34	$118.35	$118.30
7 purchase totals =	$750.02		$810.3119	$810.32	$810.40	$810.20