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	$13.84	4.121%	$14.4103	$14.41	$14.40	$14.40
Purchase #2	$136.40	9.204%	$148.9543	$148.95	$148.95	$149.00
Purchase #3	$131.32	11.639%	$146.6043	$146.60	$146.60	$146.60
Purchase #4	$147.31	5.266%	$155.0673	$155.07	$155.05	$155.10
Purchase #5	$177.34	13.291%	$200.9103	$200.91	$200.90	$200.90
Purchase #6	$89.74	3.509%	$92.889	$92.89	$92.90	$92.90
Purchase #7	$81.74	10.385%	$90.2287	$90.23	$90.25	$90.20
7 purchase totals =	$777.69		$849.0642	$849.06	$849.05	$849.10