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	$6.71	6.871%	$7.171	$7.17	$7.15	$7.20
Purchase #2	$108.53	10.159%	$119.5556	$119.56	$119.55	$119.60
Purchase #3	$146.69	12.397%	$164.8752	$164.88	$164.90	$164.90
Purchase #4	$89.98	12.219%	$100.9747	$100.97	$100.95	$101.00
Purchase #5	$23.70	6.601%	$25.2644	$25.26	$25.25	$25.30
Purchase #6	$170.49	3.462%	$176.3924	$176.39	$176.40	$176.40
Purchase #7	$75.47	4.134%	$78.5899	$78.59	$78.60	$78.60
7 purchase totals =	$621.57		$672.8232	$672.82	$672.80	$673.00