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	$11.74	5.766%	$12.4169	$12.42	$12.40	$12.40
Purchase #2	$57.31	3.535%	$59.3359	$59.34	$59.35	$59.30
Purchase #3	$39.41	5.470%	$41.5657	$41.57	$41.55	$41.60
Purchase #4	$76.26	5.509%	$80.4612	$80.46	$80.45	$80.50
Purchase #5	$9.76	6.647%	$10.4087	$10.41	$10.40	$10.40
Purchase #6	$77.60	5.478%	$81.8509	$81.85	$81.85	$81.90
Purchase #7	$28.93	7.595%	$31.1272	$31.13	$31.15	$31.10
7 purchase totals =	$301.01		$317.1665	$317.18	$317.15	$317.20